UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 


COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


CITRUS  FRUIT  INSECTS 


By  H.  J.  QUAYLE 


BULLETIN  No.  214 

(Berkeley,    Cal..    May,    1911) 


W.    W.    SHANNON       - 


SACRAMENTO 

-       -       -       SUPERINTENDENT    OP    STATE    PRINTING 

1911 


EXPERIMENT  STATION   STAFF. 


E.  J.  Wickson,  M.A.,  Director  and  Horticulturist. 

E.  W.  Hilgard,  Ph.D.,  LL.D.,  Chemist  (Emeritus). 

W.  A.  Setchell,  Ph.D.,  Botanist. 

Leroy  Anderson,  Ph.D.,  Dairy  Industry  and  Superintendent  University  Farm  Schools. 

M.  E.  Jaffa,  M.S.,  Nutrition  Expert,  in  charge  of  the  Poultry  Station. 

R.  H.  Loughridge,  Ph.D.,  Soil  Chemist  and  Physicist  (Emeritus). 

C.  W.  Wood  worth,  M.S.,  Entomologist. 

Ralph  E.  Smith,  B.S.,  Plant  Pathologist  and  Superintendent  of  Southern  California 

Pathological  Laboratory  and  Experiment  Station. 
G.   W.   Shaw,  M.A.,   Ph.D.,   Experimental  Agronomist  and  Agricultural  Technologist, 

in  charge  of  Cereal  Stations. 

E.  W.  Major,  B.Agr.,  Animal  Industry,  Farm  Manager,  University  Farm,  Davis. 

F.  T.  Bioletti,  B.S.,  Viticulturist. 

B.  A.  Etcheverry,  B.S.,  Irrigation  Expert. 

George  E.  Colby,  M.S.,  Chemist  (Fruits,  Waters,  and  Insecticides),  in  charge  of 
Chemical  Laboratory. 

H.  J.  Quayle,  M.S.,  Assistant  Entomologist,  Plant  Disease  Laboratory,  Whittier. 

W.  T.  Clarke,  B.S.,  Assistant  Horticulturist  and  Superintendent  of  University  Exten- 
sion in  Agriculture. 

H.  M.  Hall,  Ph.D.,  Assistant  Botanist. 

C.  M.  Haring,  D.V.M.,  Assistant  Veterinarian  and  Bacteriologist. 
John  S.  Burd,  B.S.,  Chemist,  in  charge  of  Fertilizer  Control. 

E.   B.   Babcock,  B.S.,   Assistant  in  Agricultural  Education. 
W.  B.  Herms,  M.A.,  Assistant  Entomologist. 

J.  H.  Norton,  M.S.,  Assistant  Chemist,  in  charge  of  Citrus  Experiment  Station,  River- 
side. 
W.  T.  Horne,  B.S.,  Assistant  Plant  Pathologist. 

J.   E.   Coit,  Ph.D.,  Assistant  Pomologist,   Plant  Disease  Laboratory,  Whittier. 
C.  B.  Lipman,  Ph.D.,  Soil  Chemist  and  Bacteriologist. 
R.  E.  Mansell,  Assistant  in  Horticulture,  m  charge  of.  Central  Station  grounds. 

A.  J.  Gaumnitz,  M.S.,  Assistant  in  Cereal  Investigations,  University  Farm,  Davis. 

E.  H.  Hagemann,  Assistant  in  Dairying,  Davis. 

B.  S.  Brown,  B.S.A.,  Assistant  in  Horticulture,  University  Farm,  Davis. 

F.  D.  Hawk,  B.S.A.,  Assistant  in  Animal  Industry. 

J.  I.  Thompson,  B.S.,  Assistant  in  Animal  Industry,  Davis. 

R.   M.   Roberts,   B.S.A.,    Field  Assistant   in  Viticulture,   University   Farm,   Davis. 

J.  C.  Bridwell,  B.S.,  Assistant  Entomologist. 

C.  H.  McCharles,  B.S.,  Assistant  in  Agricultural  Chemical  Laboratory. 
N.  D.  Ingham,  B.S.,  Assistant  in  Sylviculture,  Santa  Monica. 

E.  H.  Smith,  M.S.,  Assistant  Plant  Pathologist. 
T.  F.  Hunt,  B.S.,  Assistant  Plant  Pathologist. 

C.   O.   Smith,  M.S.,  Assistant  Plant  Pathologist,  Plant  Disease  Laboratory,  Whittier. 

F.  L.  Yeaw,  B.S.,  Assistant-  Plant  ^Pathologist,  Vacaville. 
F.  E.  Johnson,  B.L.,  M.S.,  Assis'tanVin  Soil  Laboratory. 
Charles  Fuchs,  Curator  Entomological  Museum. 

P.  L.  Hibbard,  B.S.,  Assistant  in  Fertilizer  Control  Laboratory. 
L.   M.  Davis,  B.S.,   Assistant  in  Dairy  Husbandry,  University  Farm,   Davis. 
L.  Bonnet,  LA.,  Assistant  in  Viticulture. 

S.  S.  Rogers,  B.S.,  Assistant     Plant  Pathologist,  Plant  Disease  Laboratory,  Whittier. 
B.  A.  Madson,  B.S.A.,  Assistant  in  Cereal  Laboratory. 

Walter  E.  Packard,  M.S.,  Field  Assistant,  Imperial  Valley  Investigation,  El  Centre 
M.  E.  Stover,  B.S.,  Assistant  in  Agricultural  Chemical  Laboratory. 
P.  L.  McCreary,  B.S.,  Laboratory  Assistant  in  Fertilizer  Control. 
E.  E.  Thomas,  B.S.,  Assistant  Chemist,  Plant  Disease  Laboratory,  Whittier. 
Anna  Hamilton,  Assistant  in  Entomology. 
Mrs.  D.  L.  Bunnell,  Secretary  to  Director. 
W.  H.  Volck,  Field  Assistant  in  Entomology,  Watsonville. 
E.  L.  Morris,  B.S.,  Field  Assistant  in  Entomology,  San  Jose. 
J.  S.  Hunter,  Field  Assistant  in  Entomology,  San  Mateo. 
J.  C.  Roper,  Patron,  University  Forestry  Station,  Chico. 
J.  T.   Bearss,  Foreman,  Kearney  Park  Station,  Fresno. 
MILLER,  Foreman,  Forestry  Station,  Chico. 


CONTENTS. 


INTRODUCTION.  Page. 

THE  BLACK  SCALE    (Saissetia  oleae  Bern.) 445 

Life   history   449 

Seasonal   history   451 

Distribution   and   spread 452 

Parasites  and  predaceous  enemies — 

Scutellista  cyanea  Motsch 456 

Other   enemies   459 

Control    459 

THE  RED  OR  ORANGE  SCALE   (Chrysomphalus  aurantii  Mask.) 459 

Life   history   460 

Seasonal   history    462 

Food  plants  463 

Distribution  and  spread   .. 463 

Parasites — 

Aphelinus  diaspides  How 463 

Predatory  enemies — 

Rhizobius   Lophanthw  Blaisd 464 

THE  YELLOW  SCALE  (Chrysomphalus  aurantii  var.  citrinus  Coq.) 465 

Distribution    465 

Life  history   465 

Parasites    465 

Control    ± 466 

THE  PURPLE  SCALE  (Lepidosaphes  beckii  Newm.) 466 

Life   history   466 

Seasonal   history   468 

Natural   enemies   469 

Control    469 

THE  COTTONY  CUSHION  SCALE   (Icerya  purchasi  Mask.) 469 

Present   status  in   California 470 

Life  history  annd  habits 472 

Natural   enemies   . 472 

SOFT  BROWN  SCALE   (Coccus  hesperidum  Linn.) 475 

Life  history   476 

Natural   enemies   . 476 

HEMISPHERICAL  SCALE   (Saissetia  hemisphaerica  Targ.) 478 

Natural   enemies   478 

THE  GREEDY  SCALE  (Aspidiotus  rapax  Comst.) 480 

THE  OLEANDER  SCALE   (Aspidiotus  hederae  Comst.) 481 

THE  CITRUS  MEALY  BUG  (Pseudococcus  citri  Risso.) 481 

Life  history  and  habits 483 

Natural   enemies   484 

Control    484 


CONTENTS— Continued. 

Page. 
RED  SPIDERS   (Tetranychus  mytilaspidid  Riley) 485 

(Tetranychus    sexmaculatus    Riley )_: 485 

Life  history  and  habits 486 

Control 487 

SILVER  MITE  .(Phytoptus  oleivorus  Ash.) 489 

Life  history  and  habits 489 

Control    490 

THRIPS 490 

Life  history  and  habits 493 

Control 493 

APHIS    (Aphis  gossypii) 493 

THE  ORANGE  TORTRIX  (Tortrix  citrana  Fern.) 494 

Life  history  and  habits - 495 

FULLER'S  ROSE  BEETLE  (Aramigus  fulleri  Horn.) 499 

Life  history,  habits  and  control 499 

DIABROTICA  SOROR 501 

SERIOUS  CITRUS  FRUIT  PESTS  NOT  YET  ESTABLISHED  IN  CALI- 
FORNIA     503 

The  Orange  Maggot  (Trypeta  ludens  Loew.) 503 

The  Citrus  White  Fly  (Alerodes  citri  R.  and  H.) 504 

SPRAYING  FOR  CITRUS  FRUIT  INSECTS 505 

FUMIGATION    506 

INSPECTION    AND   QUARANTINE 511 


CITRUS  FRUIT  INSECTS. 

By  H.  J.  Quayle. 


INTRODUCTION. 

That  insect  pests  are  one  of  the  important  factors  in  the  citrus  fruit 
industry  of  southern  California  is  shown  by  the  fact  that  more  than 
half  a  million  dollars  are  expended  annually  in  their  control.  This 
amount  includes  only  what  is  actually  expended  in  fumigation  and 
spraying,  and  does  not  take  into  consideration  the  loss  of  fruit  from  im- 
properly treated  trees  or  trees  not  treated  at  all.  The  cost  of  fumigation 
in  one  county  alone  amounts  to  $200,000  annually.  Furthermore,  each 
county  maintains  a  horticultural  commissioner,  and  many  of  them  a 
corps  of  inspectors,  primarily  on  account  of  insect  enemies,  who  are 
charged  with  the  quarantine  and  inspection  work,  the  cost  of  which  in 
some  of  the  counties  may  run  as  high  as  $25,000  annually.  That  all  of 
this  vigilance  is  necessary  seems  to  be  warranted  from  the  thirty  years ' 
experience  of  the  most  important  citrus  fruit  section  of  the  United 
States. 

It  has  been  estimated  that  the  average  cost  of  fumigation  per  tree, 
taking  the  whole  of  the  citrus  belt,  amounts  to  about  30  or  40  cents, 
which  means  an  expense  of  approximately  $30  to  $40  per  acre,  and  this 
is  done  on  an  average  about  every  other  year.  This  is  intensive  insect 
fighting,  but  wThen  the  improved  market  value  of  the  fruit  is  considered, 
it  is  money  judiciously  spent  with  such  a  valuable  crop  as  the  orange  or 
lemon. 

Commercial  citrus  culture  in  California  is  confined  to  seven  counties 
south  of  the  Tehachapi  mountain  range,  namely,  Santa  Barbara,  Ven- 
tura, Los  Angeles,  Orange,  Riverside,  San  Bernardino,  and  San  Diego ; 
and  the  two  counties  north  of  this  range,  namely,  Tulare  in  the  upper 
San  Joaquin  Valley,  and  Butte  in  the  upper  Sacramento  Valley.  The 
southern  counties  form  a  section  contiguous  to  the  coast  line,  and  which 
has  a  coast  climate,  excepting  the  Riverside-Redlands  district,  which 
approaches  the  interior  conditions  on  account  of  its  distance  from  the 
ocean  (60  to  75  miles),  without  being  separated  by  a  wTell-defined 
natural  barrier.  The  San  Joaquin  and  Sacramento  Valley  citrus  dis- 
tricts have  the  typically  interior  climate  which  is  characterized  by 
hotter  summers  than  that  of  the  more  equable  coast  counties. 

These  general  climatic  differences  appear  to  account  for  the  differences 
in  the  insect  pests,  not  only  of  the  northern  and  southern  sections,  but 
also  within  the  latter  section  itself,  since  even  here  there  is  a  wide  range 
of  variation.  However,  it  is  not  safe  to  speak  too  confidently  of  the 
influence  of  climate  on  insect  distribution.     Time  has  changed  a  num- 


444  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

ber  of  ideas  to  correspond  with  the  facts  as  they  exist  to-day.  It  had 
been  asserted  that  California  need  have  no  fear  of  the  citrus  white  fly, 
yet  this  pest  got  a  fairly  good  foothold  in  a  part  of  the  State  least 
unsuited  to  it,  according  to  theory.  It  was  also  held  that  the  black  scale 
would  not  exist  in  the  Riverside  section,  yet  it  occurs  there  and  attacks 
citrus  trees.  Likewise,  the  purple  was  supposed  not  to  become  a  pest 
in  arid  California,  and,  if  it  did  become  established,  it  would  be  limited 
to  a  narrower  range  than  its  distribution  at  the  present  time  indicates. 

In  general,  however,  it  may  be  said  that  the  black  scale  thrives  best 
in  sections'  near  the  coast,  as  shown  by  its  prevalence  in  the  citrus  belt 
from  Santa  Barbara  to  San  Diego,  and  also  on  deciduous  trees  in  the 
coast  counties  of  the  north.  The  interior  valley  citrus  sections  are  not 
troubled  with  the  black  scale,  though  it  may  occur  there  on  such  plants 
as  the  olive  and  oleander.  The  purple  scale,  thus  far,  is  limited  to  the 
coast  counties,  occurring  with  the  black,  but  not  of  such  wide  distribu- 
tion. The  red  and  yellow  scales  occur  both  near  the  coast  and  in  the 
interior,  though  they  are  considered  the  more  typical  scales  of  the 
warmer  interior  sections. 

Aside  from  the  scale  insects  mentioned,  the  next  most  general  citrus 
tree  pests  are  to  be  found  among  the  spiders  and  mites.  The  Florida 
red  spider  and  the  six-spotted  mite  are  widely  distributed,  while  the 
silver  mite  of  the  lemon  is  restricted  to  a  limited  section  in  San  Diego 
County.  The  mealy  bug  has  become  a  rather  serious  pest  in  certain 
limited  sections  in  Ventura  and  San  Diego  counties,  and  also  smaller 
infestations  in  other  counties.  The  soft  brown,  cottony  cushion,  and  a 
few  other  scales  sometimes  occur  in  considerable  numbers  over  small 
areas,  but  are  not  usually  considered  permanent  pests.  A  species  of 
thrips  has  recently  come  into  prominence  as  a  pest  in  the  San  Joaquin 
section.  The  orange  tortrix  is  the  only  insect  that  burrows  into  the 
orange  itself  to  any  extent,  and  this  fortunately  has  not  become  a  very 
important  pest  thus  far.  Other  insects  which  attack  the  fruit  occasion- 
ally are  grasshoppers,  katydids  and  cutworms.  Other  biting  insects 
attacking  the  leaves  only  are  .Fuller's  rose  beetle  and  the  common 
Diabrotica. 

A  couple  of  dozen  species  will  thus  cover  all  the  insects  of  economic 
importance  attacking  citrus  trees  in  California,  and  of  these,  practically 
all  of  the  control  work  is  directed  against  but  four  of  the  scale  insects, 
the  black  (Saissetia  olece  Bern.),  the  red  (Chrysomphalus  aurantii 
Mask.),  the  yellow  (Chrysomphalus  aurantii  var.  citrinis  Coq.)  and  the 
purple  (Lepidosaphes  beckii  Newm.).  The  present  publication  is 
intended  to  give  a  popular  account  of  all  those  species  likely  to  be 
considered  of  economic  importance,  together  with  their  chief  attendant 
parasites  or  enemies.  This  will  include  a  discussion  of  their  life  history 
and  habits,  mainly,  since  the  principal  reliance  for  control,  which  is 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


445 


fumigation,  is  discussed  in  separate  publications  from  this  station  and 
also  the  Department  at  Washington.  A  brief  outline  of  spraying  and 
fumigation  is,  however,  appended  at  the  close  of  this  bulletin  which  gives 
the  essential  facts  for  these  operations.  The  control  of  those  pests  which 
are  not  handled  by  fumigation  or  spraying  is  given  at  the  close  of  the 
discussion  of  each  species. 

Most  of  the  photographs  were  made  by  Professor  R.  W.  Doane  of 
Stanford  University,  who  assisted  in  the  investigation  of  citrus  fruit 
insects  during  the  summer  of  1910,  while  the  drawings  are  the  work  of 
Miss  Anna  Hamilton. 


THE    BLACK    SCALE. 

(Saissetia  olece  Bern.) 

The  Black  Scale  (Saissetia  olece  Bern.)  ranks  first  among  the  citrus 
pests  of  southern  California. 
This  statement  is  based  upon  the 
amount  of  control  work  actually 
directed  against  it,  and  its  wide 
distribution  throughout  the  cit- 
rus belt.  The  purple  scal,e  and 
the  mealy  bug  may  be  more  diffi- 
cult insects  to  control,  but  their 
distribution  is  not  so  general  as 
that  of  the  black.  In  the  county 
horticultural  commissioners '  re- 
ports tabulated  on  next  page,  the 
black  scale  is  given  first  place  in 
three  counties,  Los  Angeles,  San- 
ta Barbara,  and  Orange.  The  sec- 
ond in  two  others,  Ventura  and 
San  Diego.  While  the  mealy  bug 
is  given  first  place  in  Ventura,  it 
will  be  noticed  that  most  of  the 
control  work  is  against  the  black. 
This  scale  also  has  a  wider  dis- 
tribution in  San  Diego  County 
than  the  purple,  and  should 
probably  be  entitled  to  first 
place  there.  Where  control  work 
is  directed  against  the  purple, 
and  the  black  is  associated  with 
it,  the  extra  dosage  used  against  the  former  keeps  the  black  well  in 
check,  otherwise  it  would  have  to  be  reckoned  with  separately.     The 


Fig.  1. 


-Black  Scale  (Saissetia  oleae  Bern.) 
on  orange  twig. 


446 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


TABULAR   STATEMENT   CONCERNING   CITRUS   INSECT   PESTS   BY  COUN 


Riverside. 


R.  P.  Cundiff. 
Commissioner. 


San   Bernardino. 


S.   A.    Pease, 
Commissioner. 


Los    Angeles. 


A.   R.   Meserve, 
Commissioner. 


Orange. 

Roy  K.  Bishop, 
Commissioner. 


I.    Most  important  scale 
insect  pest  

II.    Seond   most   import- 
ant   

III.    Third    most    import- 
ant    

rv.    Annual  cost  fumigat- 
ing   


V.    Annual  cost  spraying. 

VI.    Annual  cost  fumigat- 
ing 10  years  ago 

VII.    Annual  cost  spraying 
10  years  ago 1_~ 


VIII.  Proportion  of  fumi- 
gating and  spray- 
ing for  black  scale.. 

IX.  Proportion  fumigat- 
ing and  spraying 
for  red  and  yellow.  _ 

X.  Proportion  fumigat- 
ing and  spraying 
for   purple   


XI.  Acreage      in      citrus 

fruits  10  years  ago. 

XII.  Present    acreage    __. 
XIII.    Other  control  work.. 


Red. 
Yellow. 
Black. 

$75,000 

8,000 

20,000 

5,000 

*30-40% 

60-70% 


No   purple   in 
county. 


16,000 


N.  cardinalis 
for  cottony 
cushion. 

C.  Lecanii  for 
soft   brown. 


Red. 
Yellow. 
Black. 

$200,000 

10,000 
60,000 
25,000 

33J% 


No  purple  in 
county. 


24,000 

57,000 

Spraying     for 
red  spiders. 


Black. 

Red. 

Purple. 

$175,000 

5,000 


Nearly  all. 


17,800 
29,200 


Black. 

Red. 

Purple. 

$35,000 

1,000 


12,500 


Mealy  bug  pest    Sulfur   for  red 
in  certain  sec-  spider, 

tions. 


75%  for  black  in  1910. 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


447 


TIES  GIVEN  BY  THEIR  RESPECTIVE  HORTICULTURAL  COMMISSIONERS. 


Ventura. 

San    Diego. 

Santa   Barbara. 

Butte. 

Tulare. 

E.    0.    Essig, 
Commissioner. 

C.    H.    Stuart, 
Commissioner. 

C.    W.    Beers. 
Commissioner. 

Earle  Mills. 
Commissioner. 

A.    G.    Schulz. 
Commissioner. 

Citrus  mealy 
bug. 

Purple. 

Black. 

Yellow. 

Black. 

Black. 

Purple. 

Soft  brown. 

Long-tailed 
mealy  bug. 

Citrus    mealy 
bug. 

Yellow. 



Work  just  begun. 

1908-9,    3,000 

1909-10,  10,000 

1910-11,  20,000 

$10,000 

None. 

$1,500 

None  of  the  economic 
scales  yet  estab- 
lished in  commer- 
cial groves. 

None,  except  for 
mealy  bug. 

1,000 

One  orchard 
spray. 

None. 

2,000  acres  sprayed 
for  thrips  in  1910. 

No  fumigation 
then. 

Same  as  to-day. 

No  records. 

None. 

No  fumigation 
then. 

Same  as  to-day. 

No  records. 

None. 

Practically  all. 

50% 

None. 

None  in  commer- 
cial orchards. 

Only  two  infesta- 

None. 

100% 

tions  in  county. 

1-16 

50% 

None. 

No  purple  in 
county. 

10,000 
7,000 

1,400 

1,200 
1,800 

• 

12,000 

13,000 

Lime-sulfur  for 

Scutellista      does 

Parasites  control 

Parasites       and 

red  spider. 
Predaceous     ene- 
mies:     cottony 
cushion       and 
mealy  bug. 


good  work 
some  years. 
Also  crypto- 
laemes  on 
mealy  bugs. 


Black.  Para- 
sites give  excel- 
lent control  of 
purple. 


predatory  ene- 
mies for  cot- 
tony cushion 
and  soft  brown. 


448 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


only  sections  where  the  black  is  not  considered  a  serious  pest  in  the 
south  are  certain  sections  of  Riverside  and  San  Bernardino  counties. 
The  chief  injury  occasioned  by  the  black  scale  is  not  due  so  much  to  the 
loss  of  sap  through  feeding,  nor  is  it  due  to  the  poisonous  effect  on  the 
plant  tissues  through  the  insertion  of  its  thread-like  mouth  parts.  The 
black  scale  excretes  large  quantities  of  so-called  honey  dew  which  falls 
upon  the  upper  surface  of  the  leaves  and  fruit,  and  this  serves  as  a 
medium  for  the  growth  of  a  fungus  known  as  the  sooty  mold  fungus. 
This  necessitates  the  washing  of  the  fruit,  which  operation  alone  adds 
to  the  cost  of  the  handling,  but  the  chief  injury  is  due  to  the  wash 
water  becoming  infected  with  blue  mold  and  other  fungi.  Since  the 
fruit  comes  in  contact  with  the  sides  of  the  tank,  brushes,  elevators,  and 


Fig.  2. — Mature  Black  Scales. 

drying  racks,  it  is  impossible  to  escape  some  abrasion  of  the  fruit,  into 
which  the  spores  of  the  fungus  readily  make  their  way. 

Regarding  the  washing  of  oranges,  Powell  in  Bulletin  123  of  the 
Bureau  of  Plant  Industry,  U.  S.  D.  A.,  says  the  following: 

' '  Oranges  are  washed  primarily  to  remove  the  sooty  mold  fungus  that 
grows  in  the  so-called  honey  dew  exuded  by  the  black  scale  (Saissetia 
olece  Bern.).  The  Valencia  orange  is  sometimes  washed  to  raise  the 
grade  by  making  the  fruit  clean  and  attractive,  and  the  Washington 
Navel  is  occasionally  washed  with  that  end  in  view. 

"When  the  present  investigation  by  the  Bureau  of  Plant  Industry 
was  undertaken,  from  one  third  to  one  half  of  the  oranges  of  California 
were  washed,  practically  all  the  fruit  in  some  sections  being  treated 
in  this  way,  especially  where  the  growers  had  been  over-confident  in  the 
parasite  Scutellista  cyanea  Motsch,  or  in  the  use  of  oil  sprays  as  a 
means  of  holding  the  black  scale  in  check." 

More  detailed  ;in«l  complete  publications  will  follow  on  the  Black,  Red  and  Purple 

Scales. 


Bulletin  214] 


CITRUS    FRUIT    INSECTS. 


449 


Aside  from  the  damage  to  the  fruit,  this  sooty  mold  fungus  often 
forms  a  complete  coating  over  the  surface  of  the  leaf,  which  greatly 
interferes  with  the  natural  functions  of  the  leaf  by  shutting  off  light. 
Light  is  necessary  for  the  formation  of  starch  and  sugar,  and  conse- 
quently the  sugar  content  of  the  fruit  may  be  reduced  as  a  result  of 
black  scale  infestation.  The  black  scale,  as  already  intimated,  does 
not  conspicuously  interfere  with  the  growth  of  the  tree.  There  is 
probably  no  case  where  this  insect  has  killed  a  tree,  though  some  of  the 
smaller  twigs  may  be  severely  injured.  However,  the  sooty  mold 
fungus  may  also  have  its  effect  on  the  general  growth  of  the  tree, 
because  of  its  interference  with  the  manufacture  of  sugar  which  is 
necessary  for  the  formation  of  the  living  matter  (protoplasm)  of  the 
tree. 

LIFE  HISTORY  OF   THE  BLACK  SCALE. 

The  Egg  is  almost  white  in  color  when  first  deposited,  but  later  as  it 
approaches  the  hatching  time  it  becomes  distinctly  orange.  If  the  eggs 
of  this  scale  are  placed  end  to  end  in  a 
single  line  it  will  require  about  80  to 
equal  one  inch  in  length.  The  number 
laid  varies  from  300  to  nearly  3,000, 
the  average  being  from  1,500  to  2,000. 
These  will  be  deposited  during  a  period  V 
of  two  months  during  which  time  from 
25  to  40  will  be  laid  each  day.  The 
time  required  for  the  hatching  is  from 
fifteen  to  twenty  days  during  the  spring 
or  summer  months. 

Eggs  of  this  insect  may  be  found  at 
any  season  of  the  year  in  some  section 
of  the  southern  California  citrus  belt,  FlG-  3.— Male  of  Black  Scale. 
though  the  great  bulk  of  them  are  to  be  found  in  May,  June  and  part 
of  July.  The  time  of  maximum  egg  production  in  1910  was  about  the 
second  week  in  June.  This  will  vary  from  year  to  year,  and  there 
appears  during  some  years  to  be  a  more  uniform  hatch  than  in  other 
years.  However,  practically  all  the  young  appear  by  the  middle  of 
August,  or  first  of  September,  from  that  great  majority  of  scales  that 
mature  in  the  spring. 

The  young  upon  hatching  from  the  egg  remain  beneath  the  parent 
scale  for  a  day  or  two  before  emerging.  Upon  making  their  way  from 
beneath  the  old  scale  they  actively  crawl  about  for  a  time  but  almost 
always  settle  within  two  or  three  days.  A  large  majority  settle  on  the 
leaves  or  tender  twigs.  Those  settling  on  the  leaves  rarely  come  to 
maturity  there.     As  they  become  partly  grown  they  loosen  their  hold 


450 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


and  migrate  to  the  twigs  and  branches.  The  young  scales  seem  unable 
to  become  established,  in  any  large  numbers,  on  the  older  corky  branches. 
Once  becoming  fixed  on  the  twigs  they  remain,  in  the  case  of  the  females, 
throughout  their  entire  existence.  This  migration  from  leaves  to  stems 
may  occur  when  the  scale  is  nearly  one  half  grown,  but  usually  takes 
place  prior  to  that  time. 


Fig.  4. — Leaf  on  right  showing  sooty  mold  fungus  as  a  result  of  Black  Scale 
infestation.     Normal  leaf  on  left. 

The  female  black  scale  undergoes  a  couple  of  molts,  but  the  legs  are 
not  lost  in  the  .process,  as  is  the  case  with  the  red  scale.  While  the  legs 
are  retained  throughout  its  life  they  are  functionless  after  the  scale  is 
about  one  half  grown.  It  is  during  the  growing  period,  and  partic- 
ularly as  they  approach  maturity,  that  the  honeydew  is  excreted.     It  is 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  451 

this  honeydew  that  the  ants,  which  are  so  frequently  seen  on  black  or 
soft  brown  scale-infested  trees,  are  after.  They  do  not  feed  on  the  scales, 
as  is  often  supposed,  and  neither  do  they  attack  the  tree  itself.  The  rela- 
tion of  the  ants,  therefore,  is  largely  neutral,  though  indirectly  they  may 
be  somewhat  detrimental  through  their  protection  of  the  scales  from 
parasites  and  other  enemies.  Again,  on  the  other  hand,  ants  have  been 
seen  abundant  enough,  especially  in  the  case  of  the  soft  brown  scale,  to 
take  up  all  the  honeydew  as  fast  as  it  was  excreted  so  that  the  fruit  and 
foliage  remained  clean. 

The  adult  female,  which  becomes  full  grown  in  eight  to  ten  months, 
is  hard  and  leathery  in  texture,  and  approximately  a  solid  hemisphere 
in  shape.  As  the  eggs  are  deposited  beneath,  the  tody  itself  gradually 
becomes  hollow,  so  that  when  all  the  eggs  are  deposited  the  scale  becomes 
simply  a  hollow  hemisphere  filled  with  eggs.  On  the  back  of  the  full- 
grown  scale,  and  from  the  time  it  is  half  grown  as  well,  there  is  a  distinct 
letter  H,  which  is  one  of  the  best  common  characters  for  distinguishing 
it.  The  color  varies  from  dark  brown  to  jet  black,  which  is  darker  than 
any  of  the  other  common  scale  insects  of  the  orange. 

The  male  of  this  insect  in  most  localities  has  not  been  seen,  though 
during  some  years  it  does  occur  in  considerable  numbers  in  many  sec- 
tions of  southern  California.  As  many  as  97  male  puparia  from  which 
males  had  emerged,  have  been  seen  on  a  single  orange  leaf  in  San  Diego 
County.  The  males  occur  commonly,  also,  in  Los  Angeles  and  Orange 
counties.  The  puparium  in  which  the  later  stages  of  the  male  insect 
is  passed  is  glassy  white  and  resembling  in  shape  a  partly  grown  soft 
brown  scale.  They  are  much  longer  and  narrower  than  the  female  scale 
at  the  same  stage.  The  male  which  emerged  from  those  transparent 
glass-like  scales  are  like  those  of  all  scale  insects  in  being  active  winged 
insects.  They  are,  however,  weak  fliers,  and  the  wind  may  be  an  impor- 
tant aid  in  wafting  them  from  one  tree  to  another. 

SEASONAL  HISTORY  OF  THE  BLACK  SCALE. 

There  appears  to  be  but  one  complete  generation  of  the  black  scale  in 
a  year,  and  the  majority  of  the  insects  reach  maturity  in  the  spring 
months.  The  seasonal  history  of  the  scale  differs  in  detail,  according 
to  locality.  On  citrus  trees  in  southern  California  there  is  more  or  less 
overlapping,  so  that,  in  some  sections,  the  insects  may  be  found  in  some 
of  the  stages  at  all  times  of  the  year.  Likewise,  they  may  be  found  in 
most  of  the  coast  districts  as  far  north  as  San  Francisco.  In  the  interior 
valleys,  where  the  seasons  are  a  little  more  pronounced,  more  of  the 
scales  come  to  maturity  at  a  definite  time.  Young  will  be  found  during 
the  winter  months,  but  they  are  very  few  as  compared  with  the  early 
summer  months. 

Mortality.     The  black  scale  suffers  its  greatest  mortality  during  the 


452  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

period  when  the  young  are  active,  and  again  at  the  molting  periods. 
Fully  50  per  cent  in  many  cases  fail  to  get  settled,  and  often  this  runs 
as  high  as  95  per  cent.  They  seem  unable  to  become  fixed  in  any  large 
numbers  on  stems  that  are  old  and  corky.  This  can  be  explained 
because  of  their  delicate  mouth-parts  being  unable  to  penetrate,  into 
the  harder  tissue.  But  in  those  cases,  where  they  fail  to  get  a  foothold 
on  the  leaves,  as  many  do,  and  where  there  seems  to  be  something  to 
prevent  them  from  settling,  the  matter  is  not  so  easily  accounted  for. 
In  addition  to  this  mortality,  on  account  of  the  insects  themselves,  they 
are,  of  course,  during  the  active  period  more  likely  to  be  attacked  by 
enemies  and  succumb  to  other  outside  agencies.  During  the  molting 
periods  the  insects # are  undergoing  a  profound  physiological  change, 
and  many  fail  to  pass  through  this  critical  period. 

During  the  younger  stages  of  the  insect  there  are  also  likely  to  be  hot 
weather  periods  that  kill  them  off  in  large  numbers.  Young  black 
scales  just  hatched  and  placed  on  soil  in  the  sun,  with  a  temperature  of 
108°  to  110°  in  the  sun,  died  in  1  to  1J  hours.  At  a  temperature  of 
119°  to  122°  they  died  in  15  minutes,  and  at  a  temperature  of  130°, 
died  in  5  minutes.  In  all  cases  those  under  the  same  conditions  in  the 
shade  were  not  affected.  It  is  not  uncommon  to  find  as  high  as  90  per 
cent  or  more  of  the  partly  grown  young  on  orange  leaves  killed  by  what 
appears  to  be  heat  or  other  climatic  condition. 

While,  therefore,  a  black  scale  may  lay  2,500  eggs,  and  that  would 
represent  the  progeny  at  the  end  of  the  year,  this  condition  never  obtains 
in  nature.  After  the  loss  of  first  settling,  the  loss  during  the  molts,  the 
weather,  diseases,  parasites,  and  other  enemies,  the  number  coming  to 
maturity  is  very  small  as  compared  with  the  number  of  eggs  produced. 

DISTRIBUTION  AND  SPREAD  OF  THE  BLACK  SCALE. 

The  distribution  of  the  black  scale  over  the  citrus  belt  of  the  State 
has  been  given  in  the  introduction.  It  thrives  best  in  the  coast  sections, 
and  the  reason  for  this  is  the  cooler  summers.  Often  here,  as  indicated 
above,  hot  weather  periods  bring  about  considerable  mortality,  but  not 
to  such  an  extent  as  in  the  interior  valleys.  The  black  scale  is  to  be 
found  in  greatest  numbers  on  the  underside  of  the  smaller  twigs  and 
branches  of  the  tree.  On  young  trees,  one  to  three  years  old,  they  may 
occur  even  down  on  the  trunk,  but  are  very  rarely  found  here  in  mature 
trees.  The  statement  has  been  made  that  they  occur  on  the  roots  of 
certain  plants,  such  as  the  nightshade.  "While  they  may  get  a  few  inches 
below  the  surface  in  loose  soil,  they  are  still  on  the  stem  of  the  plant  and 
are  not  to  any  extent  root-infesting  insects.  Aside  from  the  citrus  trees, 
the  olive  is  the  one  worst  infested;  in  fact,  it  attacks  the  olive  in  prefer- 
ence to  the  orange.  It  was  on  this  tree  that  the  black  scale  was  first 
discovered  and  named  by  a  Frenchman  named  Bernard  in  1782.     The 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  453 

oleander  and  pepper  are  also  favorite  host-plants  for  this  insect  in 
southern  California.  The  total  range  of  plants  attacked  is  large,  and 
includes  many  of  the  deciduous  fruit  trees  of  the  State. 

Rate  of  Travel.  The  spread  of  this  insect,  like  most  other  scales,  is 
dependent  very  largely  upon  outside  agencies  rather  than  on  its  own 
powers  for  traveling.  It  is  only  three  or  four  days  at  most  when  the 
scale  crawls  to  any  extent,  and  no  very  long  distances  can  be  covered 
by  such  a  small  insect  as  the  active  larva.  Over  smooth  paper  they  are 
capable  of  traveling  at  a  maximum  rate  of  6  feet  in  an  hour.  On  the 
basis  of  a  scale  living  four  days  and  going  at  full  speed  all  the  time  it 


Fig.  5. — Washing  oranges  to  remove  sooty  mold  fungus  which  grows  in  the 
so-called  honeydew  from  the  Black  Scale.  From  Bull.  123,  Bur.  Plant 
Industry,  U.  S.  D.  A. 

would  cover  720  feet.     But  no  scales  under  ordinary  conditions  do  this, 
nor  do  they  have  smooth  paper  to  walk  upon. 

Experiments  on  the  rate  of  travel  of  these  young  scales  over  smooth 
sand  showed  that  they  covered  a  10-inch  strip  in  from  1^  to  If  hours. 
Several  thousand  scales  were  liberated  in  the  center  of  a  4-foot  circle 
of  ordinary  orchard  soil.  The  first  scales  reached  the  edge  in  2  hours. 
Only  a  very  small  per  cent  of  the  total  number  succeeded  in  getting  over 
the  2-foot  radius  of  soil.  Similar  tests  were  made  where  the  width  of 
the  soil  to  be  traversed  was  4  feet,  but  none  came  to  the  edge  during 
the  same  day.  The  finer  the  mulch  the  more  difficult  it  is  for  travel,  and 
in  the  compacted  irrigation  furrows  they  were  found  to  make  much 
more  rapid  progress.     While,  therefore,  there  may  be  some  young  black 


454  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

scales  that  will  make  their  way  from  one  tree  to  another,  or  possibly 
to  a  second  or  third  tree  away,  by  their  own  powers  of  locomotion,  this 
means  of  transfer  must  be  considered  a  rather  small  factor  in  the  total 
spread. 

The  Wind  as  a  Factor.  The  wind  is  one  other  means  of  spreading 
scale  insects  about  which  considerable  has  been  said  with  but  little  actual 
data  presented  to  support  the  claims.  Wind  is  an  important  factor 
in  aiding  the  flight  of  small  weak  flying  insects,  as  winged  plant  lice  and 
the  winged  males  of  scale  insects;  but  it  is  not  an  important  factor  in 
the  spread  of  the  female  black  scale  in  any  stage.  The  crawling  young 
are  not  often  dislodged  from  the  tree  by  the  wind.  A  strong  current 
of  the  air  from  a  foot-bellows,  much  stronger  than  the  wind  blows  in 
this  section,  was  directed  against  a  twig  with  numerous  active  young 
black  scales.  None  were  dislodged  until  the  twig  was  brought  within 
six  inches  from  the  mouth  of  the  bellows  and  even  then  only  a  small 
proportion  were  blown  off.  Once  dislodged,  they  would  be  carried  a 
short  distance  as  they  were  falling.  From  this  and  other  experiments 
it  would  seem  to  indicate  that  it  would  be  very  unusual  for  a  scale  to  be 
dislodged  from  the  tree  by  the  wind  alone;  but  once  dislodged,  they 
would  alight  a  short  distance  further  in  the  direction  the  wind  was 
blowing.  If  the  trees  were  close  together,  they  might  alight  on  an 
adjoining  tree,  but,  with  the  navel  orange  as  ordinarily  planted,  this 
would  be  exceptional.  Of  course,  the  wind  is  an  important  means  of 
transporting  the  males  and  insuring  fecundation  of  the  females  that 
might  be  spread  by  other  means ;  but  in  the  case  of  the  black  scale,  where 
the  male  is  so  rare,  this  is  not  of  much  significance. 

Other  Agencies.  The  rapid  spread,  over  a  considerable  area,  of  such 
insects  as  the  black  scale  must,  therefore,  be  accounted  for  in  other  ways 
than  their  own  powers  of  locomotion,  or  through  the  agency  of  the  wind. 
Active  flying  or  crawling  insects  are  probably  the  most  important,  and 
of  these,  the  ladybird  beetles  must  be  considered  as  the  worst  offenders. 
These  insects  move  about  among  the  scales  themselves,  upon  which  they 
feed,  and  many  instances  have  been  observed  where  there  was  a  young 
scale  insect  on  the  backs  of  these  beetles.  About  100  of  these  beetles 
were  confined  for  a  day  in  a  jar  containing  black  scale  infested  twigs, 
and,  upon  examination,  it  was  found  that  the  young  scales  were  being 
carried  around  on  the  backs  of  the  beetles.  About  one  beetle  in  every 
ten  or  fifteen  carried  from  one  to  four  young  scales.  These  beetles,  of 
course,  fly  from  one  tree  to  another  and  the  rapid  spread  of  the  scale 
is  thus  effected.  Other  active  insects  must  also  be  considered  as  impor- 
tant, but  less  so  than  the  ladybird  beetles.  Birds,  without  doubt,  also 
spread  scale  insects,  for  these,  resting  on  scale-infested  twigs  for  a  time, 
allow  abundant  opportunity  for  the  active  young  to  crawl  upon  them. 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


455 


Because  of  the  long  flight  of  birds  they  would  be  specially  likely  to  trans- 
port them  long  distances  and  thus  account  for  isolated  scale  infestations. 

The  ordinary  operations  of  man  must  also  be  considered  as  a  factor 
in  the  spread  of  scale  insects.  Indeed,  it  has  been  through  the  trans- 
porting of  nursery  stock  that  different  species  of  scale  insects  have 
such  a  wide  distribution  over  the  world.  Practically  all  the  scales  of 
citrus  fruits  in  this  State  have  thus  been  imported  from  other  countries. 
What  applies  in  the  exchange  of  pests  between  foreign  countries,  also 
applies  between  different  states  and  also  different  counties  in  our  own 
State. 

While  nursery  stock  is  the  chief  means  of  spreading  scale  insects  long 
distances,  man  may  again  be  responsible,  through  picking  boxes,  wagons 
and  the  like,  of  spreading  scales  to  adjoining  sections  and  different 
parts  of  his  own  premises.    The  operations  of  picking  the  fruit,  through 


Fig.  6. — Drying  racks  where  fruit  is  placed  after  washing  as  a  result  of  Black 
Scale  infestation.     From  Bull.  123,  Bur.  Plant  Industry,  U.  S.  D.  A. 

wagons,  picking  boxes,  clippers,  gloves,  etc.,  and  the  movement  of  teams 
in  cultivation  may  all  aid  in  the  distribution  of  the  scale  over  the 
orchard.  Different  articles,  such  as  sticks,  boards,  rags,  and  gloves,  were 
placed  in  a  scale  infested  tree  and  allowed  to  remain  for  some  time,  and, 
upon  examination,  had  scales  crawling  over  them.  The  young  black 
scale  will  rarely  live  more  than  four  or  five  days  without  food,  so  that 
infested  articles,  such  as  picking  boxes,  if  allowed  to  remain  five  or  six 
days  or  a  week  before  carrying  into  other  groves,  there  will  not  be  much 
danger  of  infestation. 

2-B214 


456  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION. 

PARASITES  AND  PREDATORY  ENEMIES  OF  THE 
BLACK  SCALE. 

(Scutellista  cyanea  Motsch.) 

By  far  the  most  important  enemy  of  the  black  scale  in  California  is 
Scutellista  cyanea  Motsch,  introduced  into  this  State  from  South  Africa 
by  the  United  States  Department  of  Agriculture  through  Dr.  L.  0. 
Howard  in  cooperation  with  E.  M.  Ehrhorn  and  Alex.  Craw  in  1900. 
This  insect  has  become  well  established  in  most  parts  of  the  State  where 
the  black  scale  occurs.  Little,  if  anything,  therefore,  is  gained  by 
distributing  a  half  dozen  or  a  dozen  of  these  parasites  in  an  orchard 
where  they  already  occur  in  considerable  numbers,  aside  from  a  possible 
moral  effect.  In  isolated  places,  where  it  does  not  now  occur,  of  course, 
this  artificial  distribution  should  be  encouraged. 

There  is  often  a  very  great  difference  in  the  abundance  of  Scutellista 
in  different  sections  and  also  in  the  same  sections  at  different  seasons, 
it  is  not  uncommon  to  find  as  high  as  75  to  80  per  cent  of  the  scales 
parasitized  in  a  certain  section,  and  the  following  year  a  low  percentage 
of  parasitism.  There  is  considerable  irregularity,  therefore,  in  its  abun- 
dance, and  the  black  scale  still  remains  the  most  important  citrus 
fruit  pest  in  the  State.  Usually  where  there  is  a  heavy  parasitization 
by  the  Scutellista,  the  black  scale  is  very  abundant  on  the  tree.  Again, 
there  may  be  few  black  scales  and  fewer  Scutellista,  indicating  that 
other  factors  are  at  work  aside  from  the  parasite. 

We  are  accustomed  to  judge  of  the  efficiency  of  Scutellista  by  the  per- 
centage of  exit  holes  in  the  scales,  but  this  is  not  the  only  criterion. 
The  Scutellista  is  an  egg  parasite,  almost  entirely,  so  that  in  no  way 
does  it  reduce  the  injury  of  the  generation  of  scales  attacked.  The  scale 
has  come  to  maturity,  sucked  all  the  sap,  and  given  off  all  the  honeydew 
it  would  have  given  off  anyway,  whether  it  was  attacked  by  the  Scutel- 
lista or  not.  The  efficiency  of  Scutellista,  then,  must  be  judged  by  its 
power  to  reduce  the  progeny  of  the  black  scale.  It  may  seem  that  there 
ought  to  be  a  direct  relation  between  the  numbers  of  exit  holes  in  the 
scales  and  the  number  of  young  present.  But  this  is  not  necessarily 
true,  for  the  reason  that  the  Scutellista  does  not  always  consume  all  the 
eggs.  It  is  not  infrequent  to  find  a  very  high  percentage  of  exit  holes, 
and,  also,  a  great  abundance  of  young.  Cases  have  been  observed 
where  the  percentage  of  exit  holes  ran  as  high  as  75  or  80  per  cent,  yet 
on  leaves  immediately  adjoining  this,  more  than  700  young  black  scales 
were  counted  on  each.  On  healthy  trees,  and  where  all  conditions  are 
favorable  for  the  growth  of  the  scale,  they  grow  very  large,  and  a  large 
number  of  eggs  are  deposited,  more  than  enough  to  bring  the  Scutellista 
larva  to  maturity.     This,  together  with  the  fact  that  the  scales  left  unin- 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


457 


Fig.  7. — Scutellista  cyanea  Motsch,  egg  x70  ;  larva  x25  ;  pupse,  ventral  and 
dorsal  views  x20  ;  adult  xl7  ;  inverted  Black  Scale  showing  four  pupse  ;  exit 
holes    in    scales. 


458  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

festedby  the  parasite  will  produce  2,000  or  more  young,  it  is  easy  to 
account  for  the  tree  becoming  infested  again  the  following  year.  "Where 
the  scales  are  small,  the  Scutellista  larva  consumes  all  the  eggs  and  the 
number  of  young  is  greatly  lessened. 

LIFE  HISTORY  OF  SCUTELLISTA. 

The  Egg  of  the  Scutellista  is  pearly  white  in  color,  larger  in  size  than 
those  of  the  black  scale,  among  which  it  is  found,  and  has  a  long  taper- 
ing stalk  at  one  end.  They  are  deposited  under  the  black  scale  during 
the  egg  stage  or  a  little  while  previous. 

There  may  be  more  than  one  egg  deposited  under  a  single  scale 
though  apparently  not  by  the  same  Scutellista.  While  there  may  be 
several  eggs  under  one  scale  there  are  not  more  than  two,  sometimes 
three  and  very  rarely  four,  Scutellista  come  to  maturity.  The  total 
number  of  eggs  laid  is  diffcult  to  obtain  under  field  conditions.  Judg- 
ing from  experiments  in  the  insect ary  on  the  rate  of  laying  and  length 
of  adult  life,  we  are  inclined  to  put  the  maximum  at  about  25  or  30. 
The  time  required  for  hatching  is  from  five  to  six  days. 

The  Larva  is  the  familiar  white  grub-like  creature  seen  upon  lifting 
the  black  scale.  There  is  considerable  difference  in  size,  depending  upon 
the  size  of  the  scale  and  number  of  eggs.  As  stated  above,  eggs  may  be 
deposited  under  scales  without  eggs,  and  larva  have  also  been  seen 
attached  and  feeding  on  the  scale  itself.  The  larval  stage  lasts  from 
sixteen  to  twenty-one  days.  The  number  of  eggs  consumed  during  this 
period  varies  greatly.  They  are  able  to  mature  on  the  smallest  number 
laid,  which  is  500  or  less,  or  they  may  consume  2,000  or  more.  They 
feed  by  sucking  the  contents  of  the  eggs,  leaving  the  shells,  or  the  body 
juices  of  the  scale  itself. 

Pupa.  Upon  completing  its  growth  as  a  larva,  the  insect  changes 
into  the  resting  or  pupal  stage,  at  which  time  it  changes  to  a  black 
color,  and  remains  in  this  stage  from  seventeen  to  twenty  days. 

Adult.  The  adult  is  shown  in  figure  7,  and  is  the  common  metallic 
blue  fly -like  insect  seen  walking  about  on  scale-infested  twigs.  It  lives 
about  ten  days  in  this  stage. 

SEASONAL  HISTORY  OF  THE  SCUTELLISTA. 

The  life  of  the  Scutellista  is,  of  course,  dependent  upon  the  life  of  the 
black  scale.  Just  as  the  black  scale  may  be  found  somewhere  in  all 
stages  at  all  times  of  the  year2  so  will  the  Scutellista.  But,  like  the  scale 
on  which  it  is  dependent,  it  is  to  be  seen  in  greatest  abundance  in  the 
early  summer.     It  has  been  stated  that  the  maximum  egg  period  of  the 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  459 

black  scale  in  1910  was  about  the  middle  of  June.  This  was  also  the 
maximum  larval  period  for  the  Scutellista.  And  the  maximum  number 
of  adults  appeared  about  one  month  later,  or  the  middle  of  July. 

The  egg  stage  being  five  to  six  days  and  adult  life  ten  to  twelve  days, 
the  total  life  cycle  will  be  from  fifty  to  sixty  days.  These  periods  are 
under  summer  conditions,  and  in  winter  they  go  through  their  develop- 
ment much  more  slowly.  Under  favorable  conditions  there  may  be  as 
many  as  four  or  five  generations  in  a  year  in  southern  California. 

OTHER  ENEMIES   OP   THE   BLACK   SCALE. 

Another  egg  parasite  (Tomocera  California)  was  formerly  said  to 
occur  abundantly  on  the  black  scale,  but  it  has  been  of  little  significance 
of  late  years  as  compared  with  the  Scutellista.  At  the  present  time  it  is 
most  frequently  met  with  in  the  citrus  groves  of  Santa  Barbara  County. 
Several  ladybird  beetles  feed  upon  the  black  scale,  among  which  the 
most  important  is  probably  Rhizobius  ventralis,  Fig.  25.  The  steel- 
blue  ladybird  beetle  (Orcus  chalybeus)  also  occurs  abundantly  in  Santa 
Barbara  County,  where  it  feeds  on  the  black  and  also  the  yellow  scales, 
the  two  commonest  scales  of  that  section. 

THE  CONTROL  OF  THE  BLACK  SCALE. 

Aside  from  the  control  by  natural  enemies,  which  some  growers  are 
still  inclined  to  rely  upon,  fumigation,  and  in  some  cases  spraying  are 
the  standard  control  measures  for  this  scale.  For  a  brief  discussion  of 
these  measures  see  pages  505-511  of  this  bulletin. 


THE  RED  OR  ORANGE  SCALE. 

(Chrysomphalus  aurantii  Mask.) 

The  red  scale  is  the  second  most  important  citrus  fruit  scale  in  Cali- 
fornia. It  is  associated  with  the  black  in  the  coast  sections,  but  also 
occurs  beyond  the  limits  of  the  black  as  a  pest  in  the  interior.  Its  man- 
ner of  injury  differs  from  that  of  the  black  in  the  fact  that  no  honeydew 
is  given  off.  The  injury  from  the  red  scale  is  due  directly  to  the  feed- 
ing, whether  this  is  on  account  of  the  loss  of  sap,  toxic  effect  on  the 
tissues  of  the  plant,  interference  with  the  functions  of  the  stomata  when 
the  scale  is  abundant,  or  a  combination  of  these  causes.  It  is  usual  to 
speak  of  the  effect  in  the  case  of  the  San  Jose  scale  on  apple  and  pear 
because  of  the  discoloration  it  produces  in  the  tissues.  But  the  discol- 
oration is  not  evident  in  the  case  of  the  red  scale  on  citrus  trees,  though 
this  toxic  effect  may  be  present  without  producing  a  discoloration.     Of 


460 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


course,  there  is  a  discoloration  produced  on  the  leaves  in  the  form  of 
yellow  spots,  but  this  is  due  to  the  loss  of  chlorophyl,  rather  than  a 
poisonous  substance  which  reddens  the  tissue  about  the  point  of 
puncture. 

At  any  rate,  the  red  scale  which  infests  leaf,  twig,  branch  and  fruit, 
may  seriously  injure  a  tree  in  a  very  short  time.  Fig.  13  shows  a  large 
portion  of  an  orange  tree  killed  in  two  years  by  infestation  with  the  red 
scale.     In  this  respect  it  is  much  more •  virulent  than  any  of  the  other 


Fig.  8. — Red  Scale  (Chrysomphalus  aurantii  Mask.)  on  grape  fruit. 

scales  of  citrus  trees.  Aside  from  this  serious  effect  on  the  tree,  the  red 
scale  very  readily  gets  on  the  fruit,  thus  marring  its  appearance  and 
market  value. 

LIFE  HISTORY  OF  THE  RED  SCALE. 

The  Active  Young.  No  eggs  are  laid  by  the  red  scale,  so  the  starting 
point  in  the  life  history  is  the  active  young,  which  are  born  alive.  These 
are  the  minute  yellowish  creatures  which  may  be  seen  crawling  around 
on  fruit  and  leaves  infested  with  this  scale.  They  appear  somewhat 
like  granules  of  sulfur.     After  remaining  under  the  parent  scale  for  a 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


461 


day  or  two  they  emerge  and  actively  crawl  about  for  a  short  time,  but 
usually  settle  within  one  or  two  days. 

The  Fixed  Young.  As  soon  as  they  settle  they  begin  the  secretion  of 
white  cottony  fibres  with  which  they  cover  themselves.  This  later  be- 
comes more  compacted  and  reddish  in  color,  and  also  contains  parts  of 
two  molted  skins  of  the  insect.  They  remain  fixed  beneath  this  covering 
throughout  their  entire  existence.  During  the  summer  months  they 
come  to  maturity  in  about  2J  months  and  in  the  winter  from  3  to  3^ 
months. 

The  Adult  Female.  The  red  scale  is  so  called  because  of  the  reddish 
appearance  of  the  mature  scale,  but  the  reddish  color  is  almost  entirely 
in  the  scale  covering,  the  insect  beneath  being  yellow  usually.  The 
scales  are  circular  and  about  the  size  of  the  head  of  an  ordinary  pin. 
The  young  are  produced  at  the  average  rate  of  2  or  3  a  day  for  a  period 
of  two  months  in  summer.  During  the  winter  the  production  of  young 
is  almost  at  a  standstill  during  the  colder  or  wet  weather.  But  during 
a  spell  of  warm  weather  they  may  appear  in  considerable  numbers. 
Our  records  of  two  or  three  dozen  accurately  kept  for  each  day  during 
the  production  of  young,  the  number  varied  from  25  to  143  with  an 
average  of  55  for  each  scale.  The  emergence  of  young  averaged  from 
2  to  3  per  day.  During  the  colder  days  the  young  probably  remained 
under  the  parent  scale  a  little  longer,  so  that  the  maximum  or  8  were 
probably  not  born  on  the  same  day ;  though  eight  would  appear  for  two 
or  three  days  in  succession. 

Development  of  the  Male  Bed  Scale.  The  red  scale  undergoes  its  first 
molt  in  from  sixteen  to  twenty 
days  after  birth.  Up  to  this 
time  the  males  and  females 
are  exactly  alike,  but  from 
this  stage  on  they  lose  all  re- 
semblance to  one  another  and 
might  be  taken  for  different 
insects.  The  male,  after  the 
first  molt,  becomes  elongate, 
and  it  is  during  this  stage 
that  the  characteristic  elon- 
gated male  scale  covering  is 
produced.  Under  this  scale  it  changes  to  a  pro-pupa,  then  to  a  true 
pupa,  and  finally  to  the  adult,  which  is  a  frail  insect  with  two  wings. 
While  the  female  thus  undergoes  but  two  molts  and  does  not  change 
materially,  the  male  passes  through  four  molts  and  emerges  as  an  active 
insect  from  1J  to  2  months  from  birth. 


— Male  of  Red  Scale. 


462 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


SEASONAL  HISTORY  OF  THE  RED  SCALE. 

There  may  be  as  many  as  four  generations  a  year  in  southern  Cali- 
fornia. While  the 
young  from  a  single 
scale,  which  will  run 
from  40  to  80,  is  not 
nearly  so  large  as  the 
black,  the  increased 
number  of  genera- 
tions accounts  for 
them  more  rapidly  in- 
festing a  tree.  The 
first  great  production 
of  young  in  the 
spring  occurs  in  May 
and  June  and  from 
that  time  on  to  No- 
vember they  are  al- 
ways to  be  found  in 

Fig.  10. — Red  Scale,  mature  females  and  young.  large  numbers.    Scales 

matured  in  slightly  less  time  in  the  interior  section  at  Kiverside  than 
nearer  the  coast  at  Whittier. 


Fig.   11. — Red  Scale  on  orange  leaf. 


The  greatest  mortality  occurs  during  the  active  period  of  the  young. 
In  all  our  breeding  experiments  the  per  cent  would  average  about  40. 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


463 


FOOD  PLANTS. 

While  the  red  scale  is  essentially  a  citrus  pest  it  is  known  to  attack 
other  plants,  including  some  of  the  deciduous  fruit  trees;  but  in  Cali- 
fornia it  is  of  little  consequence  outside  of  the  citrus  fruits.  A  more 
or  less  common  weed,  in  poorly  cared  for  California  orchards,  is  the 
nightshade,  and  this  plant  is  readily  attacked  by  this  scale.  Ivy  is 
another  often  attacked. 

DISTRIBUTION  AND  SPREAD  OF  THE  RED  SCALE. 

The  maximum  rate  of  travel  of  young  red  scales  over  smooth  surfaces 
is  at  the  rate  of  4^  feet  per  hour.  The  rate  of  travel  over  orchard  soil, 
where  there  is  a  fine  mulch,  is  practically  negligible.  We  have  not  suc- 
ceeded thus  far  in  getting  them  across  a  3-inch  strip  of  such  soil.  If 
these  young  scales  are  watched  closely,  they  will  be  seen  to  nearly  always 
fall  back  in  their  attempt  to  ascend  a  small  particle  of  earth.  Thus  they 
are  able  to  make  no  progress,  and  one  kept  under  constant  observation 
did  not  travel  half  an  inch  in  two  hours.  If  there  is  a  fine  mulch  in  the 
grove,  as  most  are  kept  in  California,  there  is  little  danger  of  the  spread 
of  the  red  scale  as  dependent  upon  their  own  powers  of  locomotion.  But 
here  again,  if  the  soil  is  compacted,  as  in  irrigation  furrows  or  after  a 
rain,  they  can  travel  very  well. 

Other  points  taken  up  under  the  head  of  "Distribution  and  Spread 
of  the  Black  Scale"  also  applies  for  the  red. 


PARASITES  OF  THE  RED  SCALE. 

(Aphelinus  diaspidis  Howard.) 

The  commonest  parasite  of  the  red  scale,  and  the  only  one  of  any 
economic  significance,  is  the  little  chalcid  {Aphelinus  diaspidis  How- 
ard). This  parasite  is  well  distributed  over  the  citrus  belt,  but  since 
the  highest  parasiti-  r*t«T-^  r**»£ 

zation    seen    during  v_        j^/f3^^"^^ 

the  past  three  years 
would  not  exceed  5 
or  10  per  cent,  it  is 
of  little  consequence 
as  a  control  factor. 

The  egg  of  this 
parasite  is  deposited 
beneath  the  scale, 
and  the  grub-like 
larva  upon  hatching  FlG 
attaches  itself  to  the 
scale  and  sucks  the  body  juices 


12.- 


Aphelinus  diaspidis  How. 
Yellow  Scales. 


Parasite  on  Red  and 
x39. 


It  is  not,  therefore,  an  internal  para- 


464 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


site,  for  at  no  stage  is  it  within  the  body  of  the  scale  insect  itself.  The 
eggs  hatch  in  five  to  seven  days ;  the  larva  grows  to  maturity  in  twelve 
to  sixteen  days ;  it  is  eight  to  ten  days  in  the  pupal  stage,  and  lives  as 
an  adult  four  or  five  days.  The  number  of  eggs  deposited  is  not  large, 
and  probably  will  not  exceed  25  or  30. 


Fig.  13. 


-Large  portion  of  orange  tree  killed  as  result  of  two 
years'  infestation  of  Red  Scale. 


There  are  certain  of  the  ladybird  beetles  that  feed  on  the  red  scale, 
the  commonest  being  a  small  black  species  (Bhizobius  lophanthce)  shown 
in  Fig.  25.  The  eggs  of  this  beetle  may  be  laid  beneath  the  scales,  but 
the  larva  upon  hatching  travels  about,  attacking  many  different  insects. 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  465 


THE  YELLOW  SCALE. 

(Chrysomphalus  aurantii  var.  citrinus.) 

This  scale  is  very  similar  in  appearance  to  the  red  scale,  and  in  the 
absence  of  typical  specimens,  or  considerable  material,  it  is  impossible 
to  distinguish  the  two.  The  structural  characters  of  the  insects  them- 
selves are  identical.  But  the  scales  as  seen  on  the  tree  are  usually  not 
difficult  to  determine.  The  yellow  is  distinctly  lighter  in  color,  lies 
flatter  upon  the  leaf,  and  is  often  slightly  larger  in  diameter.  When 
the  yellow  scale  dies,  the  scale  covering  becomes  darker  in  color,  in 
which  case  they  are  much  more  difficult  to  separate. 

But  aside  from  this  difference  in  general  appearance  there  is  a 
distinct  variance  in  habits.  The  red  scale  attacks  all  parts  of  the  tree, 
whereas,  the  yellow  is  limited  almost  entirely  to  the  leaves  and  fruit. 
Leaves  may  be  very  badly  infested  with  the  yellow,  and  but  an  occa- 
sional scale  on  the  twigs,  while  in  the  case  of  the  red,  the  twigs  and 
branches  really  become  infested  first.  Because  of  the  fact  that  the 
twigs  are  not  attacked  its  power  to  injure  the  tree  is  not  so  great,  and 
it  can  not  be  counted  as  serious  a  pest  as  the  red. 

DISTRIBUTION    OF    THE    YELLOW    SCALE. 

The  yellow  scale  occurs  scatteringly  over  practically  the  whole  of 
the  citrus  belt  in  southern  California,  having  much  the  same  distribu- 
tion as  that  of  the  red ;  but  in  the  Sacramento  Valley  citrus  section  it 
appears  to  occur  exclusively,  there  being  no  red  to  the  writer's  knowl- 
edge thus  far  seen  in  that  section. 

LIFE   HISTORY. 

The  life  history  of  the  yellow  scale  is  the  same  in  all  particulars  as 
the  red,  so  that  it  need  not  be  repeated  here. 

PARASITES  AND  PREDACEOUS  ENEMIES. 

The  parasite  discussed  in  connection  with  the  red  scale  also  attacks 
the  yellow.  But  there  is  another  common  parasite  of  the  yellow,  and 
which,  in  former  years,  was  said  to  be  a  very  effective  check  on  this  scale. 
Many  people  still  believe  that  the  disappearance  of  the  yellow  scale  in 
places  where  it  was  once  much  more  prevalent  than  now  was  due  to  the 
work  of  this  parasite.  There  is  no  doubt  that  the  early  reports  con- 
cerning this  parasite  were,  like  many  others,  greatly  exaggerated  and 
based  upon  no  careful  observations.  This  parasite  of  the  yellow  scale 
has  the  scientific  name  of  Aspidiotiphagus  citrinus  Craw.  It  is  strictly 
an  internal  parasite,  living  with  the  body  of  the  scale  insect  itself,  and 


466 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


emerging  when  about  half- grown.  At  the  present  time  it  is  most  abun- 
dant in  Santa  Barbara  County,  and  counts  made  show  that  as  high  as 
25  per  cent  of  the  scales  may  be  parasitized. 

The  control  of  the  red  and  yellow  scales  is  effected  by  fumigation, 
for  which  see  the  close  of  this  bulletin. 


THE    PURPLE    SCALE. 

(Lepidosaphes  beckii  Newm.) 

The  purple  scale  was  introduced  in  California  upon  cuttings  from 
Florida  in  1892.  Statements  were  then  made  that  it  would  not  thrive 
in  the  drier  California  climate,  but  it  has  succeeded  very  well  in  many 
of  the  coast  sections  from  Santa  Barbara  to  San  Diego.  Its  eastern 
limit  at  present  is  in  the  eastern  part  of  Los  Angeles  County,  and  has 
not  yet  appeared  in  Riverside  or  San  Bernardino  counties,  nor  any  of 
the  northern  citrus  sections. 

The  purple  scale  is  the  most  difficult  to  handle  of  the  four  scales  thus 


Fig.  14. — Purple  Scale  on  orange  leaf. 

far  mentioned,  because  of  the  resistance  of  the  eggs  to  fumigation.  It 
attacks  leaf,  branch,  and  fruit,  often  becoming  incrusted  on  but  a 
portion  of  the  tree,  usually  the  lower  side.  Parts  of  the  tree  will  thus 
be  badly  injured  by  the  dropping  of  the  leaves  and  the  killing  of  the 
branches,  but  it  seldom,  if  ever,  destroys  the  entire  tree.  The  retention 
of  the  scales  on  the  fruit  after  it  comes  into  the  packing  house  is  another 
point  against  the  purple  scale. 

LIFE  HISTORY  OF  THE  PURPLE  SCALE. 

The  eggs  of  the  purple  scale  are  the  pearly  white  oval-shaped  bodies, 
which  are  to  be  seen  upon  lifting  the  mature  scales.     They  are  almost 


Bulletin  214] 


CITRUS   FRUIT    INSECTS. 


467 


completely  enclosed  by  the  firm  scale-covering  above  and  the  lighter 
cotton-layer  beneath,  forming  a  sack  with  the  opening  at  the  posterior 
tip,  through  which  the  young  make  their  escape.  It  is  for  this  reason, 
largely,  that  the  purple  scale  eggs  are  so  resistant  to  hydrocyanic  acid 
gas  on  account  of  the  difficulty  of  the  gas  reaching  them. 

The  number  of  eggs  deposited  is  from  30  to  40  extending  over  a  period 
of  three  or  four  weeks.  The  eggs  hatch  in  fifteen  to  twenty  days  during 
the  summer  months.  From  the  time  the  eggs  first  appear  until  the  last 
ones  hatch,  therefore,  is  a  period  of  about  two  months,  so  that  about 
six  weeks  or  two  months  ought  to  be  allowed  between  fumigations,  where 


Fig.  15. — Purple  Scale  on  orange  leaf  enlarged. 

two  treatments  are  made,  as  sometimes  is  done  with  this  scale.  The 
most  eggs  are  present  in  the  spring  or  early  summer  (May  and  June) 
though  all  through  the  season  they  may  occur  in  all  stages. 

The  Young.  The  young  scales  upon  hatching  remain  under  the 
parent  but  a  day  or  two,  and  after  another  day  or  two  of  actively  moving 
about  over  the  plant,  they  settle  down  and  remain  stationary,  in  the 
case  of  the  female,  throughout  the  rest  of  their  lives.  They  first  secrete 
a  couple  of  coarse,  entangling  threads,  which  serve  as  protection  until 
they  have  opportunity  to  cover  themselves  with  the  permanent  scale 
covering. 

The  female  undergoes  two  molts  within  a  period  of  one  to  one  and  a 
half  months.     Eggs  will  be  deposited  at  the  end  of  two  months  in  sum- 


468 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


mer,  and  during  winter  it  is  prolonged  to  three  and  over.  Young  will 
begin  appearing  in  a  little  less  than  three  months  from  the  time  the 
parent  was  an  active  young  scale.  The  old  scale  dies  soon  after  the 
production  of  eggs. 

The  male  purple  scale,  after  molting  four  times  and  going  through 
the  usual  pro-pupal  and  pupal  stages,  emerges  as  a  winged  insect  after 
a  period  of  approximately  two  months  in  summer  and  three  months  in 
the  winter  season.  The  scale  of  the  male  is  long  and  narrow  and  easily 
distinguished  from  that  of  the  female. 


Fig.  16. — Orange  incrusted  with  Purple  Scale. 


SEASONAL  HISTORY  OF  THE  PURPLE  SCALE. 

Taking  the  minimum  period  from  young  to  young  in  midsummer  at 
80  days  and  the  maximum  in  winter  at  120  days,  there  will  appear 
during  the  season  between  three  and  four  generations  of  the  purple 
scale.  In  the  case  of  warmer  dry  winters  there  may  be  four  full  genera- 
tions in  the  year.  There  appears  to  be  a  maximum  period  of  eggs  and 
young  in  May  and  June,  and  again  in  August  and  early  September. 
The  season  of  greatest  mortality  is  here  again  coincident  with  the  season 
of  greatest  production  of  young ;  but  a  larger  portion  of  the  young  suc- 
ceed in  getting  established  than  is  the  case  with  either  the  red  or  the 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  469 

black  scales.  The  provision  for  mortality,  as  indicated  by  the  number  of 
eggs  produced,  is  not  so  great  as  in  the  black  scale,  for  the  black  scale 
produces  fifty  times  more  eggs  than  the  purple. 

NATURAL  ENEMIES  OF  THE  PURPLE  SCALE. 

Aspidiotiphagus  citrinus  Craw,  is  the  only  parasite  we  have  thus  far 
taken  from  the  purple  scale.  This  is  strictly  an  internal  parasite,  and 
attacks  the  scale  only  between  the  first  and  second  molts.  The  egg  is 
deposited  within  the  insect,  and  there  hatches  a  very  minute  white 
larva  with  a  tail-like  appendage,  which  disappears  with  the  later  molts. 
The  adult  makes  its  way  out 
through  a  circular  exit  hole 
in  the  posterior  one  third  of 
the  scale. 

This  parasite  is  not  gen-    ^ 
erally  distributed  over  the 


localities  where  the  purple 
scale  occurs,  and  it  is  only 
occasionally  that  the  parasite 
will  be  met  with ;  but  where 

it  does  OCCUr,  the  amount  Of    Fl?;    ^ --^pidwUphagus    citrinus    Craw        x40. 

Parasite   on    Purple,    Yellow,   and   Red   Scales. 

parasitization    may    run    as 

high  as  30  or  40  per  cent.  During  the  winter  months  it  has  taken  at 
least  five  days  for  the  eggs  to  hatch  and  nine  weeks  are  necessary  for  its 
complete  life  cycle.     In  summer  it  requires  much  less  time. 

In  addition  to  this  internal  parasite  several  kinds  of  ladybird  beetles 
may  be  occasionally  seen  to  feed  upon  the  purple  scale,  and  the  com- 
monest of  these  are  Bhizobius  lophanthce  Blaisd.  and  Scymnus  margi- 
nicolles. 

For  the  control  of  the  purple  scale,  see  discussion  on  fumigation  on 
page  506. 

THE  COTTONY  CUSHION  SCALE. 

{I  eery  a  purchasi  Mask.) 

The  cottony  cushion  scale  is  a  native  of  Australia  and  was  introduced 
into  California,  probably  upon  an  acacia  at  Menlo  Park,  in  1868. 
Twenty  years  later  it  was  widely  spread  over  the  State  and  considered 
a  very  serious  menace  to  the  citrus  fruit  industry.  In  1889,  the  Austra- 
lian ladybird  beetle  (Novius  cardinalis)  was  introduced  through  the 
efforts  of  the  Division  of  Entomology  of  the  United  States  Department 
of  Agriculture.  In  a  short  while  it  was  reported  to  have  the  scale  under 
subjection,  and  has  usually  apparently  kept  it  so  ever  since. 

This  importation  has  always  been  referred  to  as  the  most  successful 
case  on  record  of  one  insect  keeping  another  under  control.     In  fact,  it 


470 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


has  been  the  stimulus,  the  support,  and  the  hope  for  the  future,  for  a 
large  amount  of  work  along  the  line  of  importing  one  insect  to  prey  upon 

another.  This  has  been  espe- 
cially true  in  this  State,  and 
while  much  good  work  may 
have  been  done,  there  has  not 
been  approached  any  such 
signal  success  as  seemed  to 
be  the  case  with  cardinalis. 

PRESENT  STATUS  OF  THE  COT- 
TONY CUSHION  SCALE  IN 
CALIFORNIA. 

"While  the  cottony  cushion 
scale  is  at  present  a  pest  of 
comparatively  little  conse- 
quence, it  is  still  one  of  the 
commonest  insects  inquired 
about  throughout  the  entire 
length  of  the  State  where 
citrus  trees  are  grown. 
While  the  cardinalis  is  pret- 
ty well  distributed  over  the 
State,  and  often  appears  un- 
aided in  an  infestation  of 
cottony  cushion  scale,  yet  in 
many  cases  it  does  not  occur, 
and  neither  does  the  scale 
become  very  abundant.  The 
checking  of  the  scale  in  such 
cases  must  be  accounted  for 
through  some  other  factors. 
Sometimes,  too,  the  beetle  is 
slow  in  getting  the  scale 
under  control.  On  the  sta- 
tion grounds  at  Riverside 
fifty  or  seventy-five  orange 
trees  have  been  infested 
with  the  cottony  cushion 
scale,  as  bad  as  occurred 
when  the  insect  was  at  its 
height,  for  at  least  four 
years.  During  this  time  also  the  ladybird  beetle  has  been  present.  The 
scale  becomes  very  abundant  each  spring,  when  the  cardinalis  begins 


Fig.  18 


-Cottony  Cushion  Scale  on  orange 
twig. 


Bulletin  214] 


CITRUS    FRUIT   INSECTS. 


471 


work  and  effectively  checks  them.     The  beetles  are  present  in  April, 
May,  and  June,  and  disappear  in  July.     Some  young  scales  are  left 


..^t^MHHKSSMHPQMto^, 

•£^sy5w 

^igtfjjl         jltfvi^tfofr 

Fig.  19. — Young  Cottony  Cushion  Scales  on  orange  leaf.     Larva  and  adult  of 
the  Australian  ladybird  beetle  also  shown  feeding  upon  the  scales. 


Fig.   20. — Different  stages  in  the  development  of  the  Cottony  Cushion 

Scale. 


and  those  have  a  chance  to  multiply  and  severely  infest  the  tree  again 
before  the  cardinalis  appears  in  the  spring.  This  has  been  the  history 
of  the  infestation  for  the  past  four  years. 


3— B214 


472 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


LIFE  HISTORY  AND  HABITS  OF  THE  COTTONY  CUSHION  SCALE. 

The  large  fluted  cottony  mass  that  is  so  characteristic  of  this  scale  is 
secreted  only  by  the  female  when  it  is  full  grown.  This  is  for  the 
protection  of  the  orange  yellow  eggs  that  are  deposited  within  the  mass 
and  which  is  enlarged  as  the  500  to  800  eggs  are  deposited.  These 
require  ten  to  twelve  days  to  hatch  in  summer  and  may  be  prolonged 
to  three  weeks  in  winter. 

The  larvae  settle  upon  the  leaves  and  twigs,  arranging  themselves 
largely  along  the  mid  rib  and  veins  of  the  leaf.  In  the  later  stages 
they  prefer  the  twigs  and  branches,  or  even  the  trunk.  Occasionally, 
they  develop  on  the  leaves,  but  very  rarely  upon  the  fruit.  Unlike  the 
other  scales  mentioned,  the  cottony  cushion  scale  travels  throughout  the 
greater  part  of  its  life,  or  until  the  egg  sack  is  secreted. 

There  is  a  great  variation  in  the  time  of  development  of  the  different 

scales,  even  during  the  same  season. 
Some  will  mature  in  three  months, 
while  others  will  go  four  months 
and  over.  There  are  about  three 
generations  a  year  in  southern 
California,  but  on  account  of  the 
irregularity  in  development  these 
are  not  at  all  distinct.  The  season 
of  greatest  production  of  young  is 
May  and  June.  The  injury  from 
this  scale  is  due  to  the  honeydew  given  off,  and  also  to  the  direct  attack 
upon  the  tree. 


Fig.    21. — Male  of  Cottony  Cushion 
Scale. 


NATURAL  ENEMIES  OF,  THE  COTTONY  CUSHION  SCALE. 

Novius  cardinalis,  the  Australian  ladybird  beetle,  is  the  most  effective 
enemy  of  the  cottony  cushion  scale,  and  in  most  cases  may  be  relied 
upon  to  control  it.  The  adult  beetle  lays  from  150  to  200  orange  red 
eggs,  most  usually  in  the  cottony  egg  sack.  These  hatch  in  five  or  six 
days  and  the  larvae  begin  at  once  to  feed  upon  the  eggs.  .  Later,  they 
feed  upon  all  stages  of  the  scale  and  their  growth  as  a  larva  is  completed 
in  three  weeks.  The  pupal  stage  lasts  about  a  week,  wljen  the  adult 
beetle,  with  red  and  black  markings,  appears.  This  beetle  is  known  to 
feed  only  upon  the  cottony  cushion  scale,  or  their  own  kind,  if  food 
becomes  scarce.  For  this  reason,  upon  the  cleaning  up  of  an  infestation 
of  scale,  the  beetles  themselves  often  die,  so  that  there  is  cause  for 
maintaining  a  supply  and  sending  them  out  to  new  infestations. 

Another  enemy  of  the  scale  is  the  dipterous  or  two-winged  parasite 
(Cryptochcetum,  iceryce  Will.).  This  is  said  to  have  occurred  quite 
abundantly  in  former  years,  but  is  no  longer  considered  an  important 


Bulletin  214] 


CITRUS    FRUIT   INSECTS. 


473 


aid  in  the  control  of  the  scale.     This  is  a  small  black  fly  with  green 
metallic  reflections.     The   larva   lives   with   the   scale    and   the    adult 


Fig.  22. — Exudation  or  honeydew  from  Cottony  Cushion  Scale  crystallized 
and  before  growth  of  fungus  has   started. 


V                     TBI 

Si 

J 

if* 

■ 

l_ 

1 

Fig.  23. — Pupae  of  N.  cardinalis  on  orange  tree. 


Fig.  24. — Different  stages  of  the  larva  of  N.  cardinalis. 

emerges  through  an  exit  hole,  which  characterizes  those  scales  parasi- 
tized.    Infestations  of  this  scale  very  often  occur  with  no  evidence  of 


474 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


the  parasite,  showing  that  its  distribution  is  not  so  general  as  that  of 
many  others.  It  has  been  most  frequently  met  with  during  the  past 
two  or  three  years  in  Santa  Barbara  and  Orange  counties. 

The  main  reliance  for  control,  therefore,  is  the  ladybird  beetle 
(Novius  cardinalis)  and  if  specimens  are  not  already  present  among 
the  scales  they  may  usually  be  obtained  from  the  State  Insectary, 
Sacramento. 


>,     tf""^*    I  A1 


LO 


Fig.  25. — Some  common  ladybird  beetles.     All  enlarged  5  times. 

1.  Scymnus  marginicollis,  Mann.,  feeding  on  Red  and  Purple  Scales. 

2.  Rhizobius  lophanthae,   Blaisd.,   feeding  on  Red  and  Purple  Scales. 

3.  Scymnus  nebulosis,  Lee.,  feeding  on  Red  and  Yellow  Scales. 

4.  Rhizobius  sp.  feeding  on  Purple  Scale. 

5.  Hyperaspis,   8  notata,   on  Monterey  Pine  Scale. 

6.  Novius  koebeli,  Oliv.,  feeding  on  Red  Scale. 

.7.  Rhizobius  ventralis,  Black,  feeding  on  Black  Scale. 

8.  Orcus  chalybeus,  Boisd.,  feeding  on  Black,  Red,  Yellow,  and  Purple. 

9.  Novius  cardinalis,  Black,  feeding  on  Cottony  Cushion. 
10.   Cryptolsemus  montrouzeri,   feeding  on  Mealy  Bug. 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


475 


Fig.  26. — Some  common  ladybird  beetles,  all  enlarged  five  times. 

1.  Olla  plagiata,  Casey,  feeding  on  Aphids. 

2.  Axion  plagiatom,  Casey,  feeding  on  Black  Scale. 

3.  Hippodamia  convergens,  Guer.,  feeding  on  Aphids  and  scale  insects. 

4.  Coccinella  calif ornica,  Mann,  feeding  on  Aphids  and  scale  insects. 

5.  Hippodamia  ambigua,  Lee,  feeding  on  Aphids  and  scale  insects. 

6.  Hippodamia  ambigua,  Lee,  feeding  on  Aphids  and  scale  insects. 


SOFT   BROWN   SCALE. 

(Coccus  hesperidium  Linn.) 
This  scale,  while  seldom  occurring  in  injurious  numbers  over  an  entire 
orchard,  often  severely  infests  an  occasional  tree  or  portion  of  a  tree; 
but  the  infestation  is  usually  of  short  duration,  due,  in  most  cases  to 


476 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


the  efficient  Avork  of  one  or  two  parasites.  This  scale  is  thoroughly 
distributed  over  the  world,  and  attacks  a  large  number  of  widely  dif- 
ferent plants.  Its  injury  is  due  chiefly  to  the  copious  amount  of  honey- 
dew  given  off,  and  the  consequent  growth  of  the 
sooty  mold  fungus.  It  attacks  the  smaller  twigs 
and  the  leaves. 

LIFE  HISTORY  AND  HABITS  OF  THE  SOFT  BROWN  SCALE. 

No  eggs  are  deposited  by  this  scale,  the  young 
being  born  alive,  as  is  the  case  with  the  red  scale. 
The  active  young  soon  settle  and  remain  fixed, 
though  there  may  be  some  movement  until  it  is 
about  one  half  grown.  They  molt  twice  and  come 
to  maturity,  and  produce  young  in  sixty-five  days 
during  the  summer  months.     The  largest  number 


7W^^i^\^0m 


.^ 


Fig.   28. 


-Aphycus  flavus  How.   parasite  or  soft  brown 
scale.     x40. 


Fig.  27. — Soft 
brown  scale 
on  orange 
twig. 

summer  months. 
and  five. 


of  young  we  obtained  from  a  single  scale  has  not 
exceeded  30  distributed  over  a  period  of  thirty  to 
thirty-five  days.  There  may  be,  thus,  several  gen- 
erations in  a  year,  but  during  the  winter  their 
development  is  very  slow.  The  young  usually  ap- 
pear abundantly  in  May,  and  again  in  July,  and 
also  in  September,  but  on  account  of  the  overlap- 
ping, many  may  be  present  continually  during  the 
The  total  number  of  generations  will  be  between  four 


NATURAL  ENEMIES  OF  THE  SOFT  BROWN  SCALE. 

There  are  two  common  internal  parasites  of  the  scale,  Coccophagus 
lecanii  Fitch,  and  Aphycus  flavus  How.  The  former  emerges  when  the 
scale  is  nearly  grown  or  of  considerable  size,  while  the  latter  emerges 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


477 


usually  while  the  scale  is  still  small,  not  more  than  half  grown.  Those 
scales  parasitized  with  lecanii  may  be  known  when  the  parasite  is  in  the 
pupal  stage  by  the  black  color  which  is  shown  through  the  scale.     The 


Fig.   29. — Coccophagus  lecanii,  Fitch,  parasite  of  soft  brown  and 
other  scales. 

other  parasite  is  yellowish  in  color,  and  does  not  make  the  scale  appear 
black.     These  are  strictly  internal  parasites  and  the  Aphycus  is  the 


Fig.  30. — Soft  brown  scales  with  exit  holes  of 
parasites.  Partly  grown  scale  shown  at  top  of 
figure. 

more  effective  when  abundant  because  the  scales  are  checked  before 
they  attain  any  size.  The  scale  is  often  alive  for  some  time  after  the 
parasite  has  changed  to  the  pupa.  Other  parasites  taken  from  this  scale 
are  Encrytus  flavus  and  Coccophagus  lunulatus. 


478 


TXIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


HEMSIPHERICAL  SCALE. 

(Saissetia  kemisphaerica  Targ.) 


Fig.   31. — Hemispherical  scale,  Saissetia  hemisphaerica, 
on  leaf  of  Christmas  berry. 

absence  of  the  letter  H,  its  lighter 
color  of  brown,  and  its  smooth 
shiny  surface.  Full  grown  scales 
of  this  species  are  commonly 
found  on  the  leaves  as  well  as  the 
twigs,  and  some  have  the  habit 
of  settling  on  the  very  edge  of 
the  leaf. 

NATURAL   ENEMIES   OF    THE    HEMIS- 
PHERICAL  SCALE. 

Coccophagus  lecanii,  the  same 
internal  parasite  that  attacks  the 
soft  brown  scale,  also  attacks  the 
Hemisphaerica  scale  and  emerges 
from  the  scale  when  about  one 
half    grown.      Another    parasite, 


This  is  a  scale 
that  is  of  little  con- 
sequence as  a  citrus 
tree  pest,  though  it 
is  commonly  found 
on  such  trees  in 
certain  sections  as 
Santa  Barbara  and 
San  Diego.  It  is 
essentially  a  green- 
house scale,  but 
thrives  out  of  doors 
in  mild  climates. 
Here,  in  California, 
it  more  readily  at- 
tacks certain  orna- 
mental plants,  as 
the  Christmas  ber- 
ry, oleander,  and 
palm.  It  is  easily 
distinguished  from 
the  black,  which  is 
its  nearest  ally  on 
citrus  trees,  by  the 


Fig.   32. 


Hemisphaerica  scale  on  leaf 
of  orange. 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


479 


Comys  fusca,  is  found  commonly  in  this  scale,  and  this  one  emerges 
when  the  scale  is  nearly  or  quite  full  grown.     Scutellista  cyanea,  the 


T  ^'■^S^m 

11 

™*aS 

Fig.   33. — Hemispherical   Scale 
on   twig  of  orange. 


Fig.   34. — Male  puparia  of  Hemispher- 
ical Scale. 


Fig.   35. — Comys  fusca  How.,  parasite  on  Hemispherical,   Brown  Apricot, 
and  other  scales.     xl8. 


egg  parasite  of  the  black  scale,  also  occurs  occasionally  in  this  scale,  as 
well  as  some  of  the  other  internal  parasites. 


480 


UNIVERSITY   OP    CALIFORNIA EXPERIMENT    STATION. 


THE  GREEDY  SCALE. 

(Aspidiotus  rapax  Comst.) 

This  scale  sometimes  infests  the  twigs  of  citrus  trees  and  also  com- 
monly occurs  on  the  older  fruit  that  may  be  still  remaining  on  the  tree 


Fig.  36. — Orange  Infested  with  Greedy  Scale  (Aspidiotus  rapax,  Comst.), 


from  the  previous  year,  or  the  older  tree-ripe  lemons.  It  is  thus  on  the 
older  fruit  that  this  insect  attracts  most  attention,  and  so  long  as  it  is 
confined  to  such  fruit,  the  injury  is  of  little  consequence.  But,  occa- 
sionally, it  will  also  be  found  on  marketable  fruit  and  is  often  associated 
in  scattering  numbers  with  other  scales.  It  may  be  distinguished  from 
the  red  or  yellow  by  its  lighter  gray  color  and  its  much  greater  con- 
vexity. The  greedy  scale  infests  a  long  list  of  plants  and  occurs  more 
abundantly  on  acacia,  laurel,  and  other  shade  and  ornamental  trees 
than  upon  citrus  trees.  The  parasite  Aphelinus  fuscipennis  How.,  has 
been  bred  in  some  numbers  from  this  scale. 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


481 


THE  OLEANDER  SCALE. 

(Aspidiotus  hederce  Comst.) 

This  scale  is  known  as  a  citrus  fruit  scale  because  of  its  occasional 
occurrence  on  lemons,  and  goes  by  the  common  name  of  Lemon  Peel 


Fig.   37. — Oleander  Scale    (Aspidiotus  hederse). 

Scale.     It  does  no  injury  particularly  to  the  tree,  and  is  mentioned 
here  because  it  is  sometimes  met  with  on  the  fruit. 


THE  CITRUS  MEALY  BUG. 

(Pseudococcus  citri  Risso.) 

The  citrus  mealy  bug  is  widely  distributed  over  the  citrus  trees  of  the 
State  from  Chico  to  San  Diego,  but  it  is  considered  an  important  pest 
only  in  certain  restricted  localities,  notably  in  Ventura  and  San  Diego 
counties.  It  is  also  found  commonly  on  the  citrus  trees  of  the  Sacra- 
mento and  San  Joaquin  valleys.  It  has  been  known  to  occur  in  the 
State  for  the  past  fifteen  or  twenty  years,  but  has  never  been  consid- 
ered a  very  serious  pest,  except  recently  in  San  Diego  and  Ventura  and 
to  a  less  extent  in  other  counties.     The  mealy  bug  is  an  insect  that 


482 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


approaches  the  extent  of  a  pest  more  or  less  periodically,  and  in  many 
cases  where  it  is  present  for  a  few  years  will  disappear  without  any  well 
known  specific  causes. 

The  mealy  bug  attacks  all  parts  of  the  tree,  leaf,  branch,  and  fruit, 


Fig.  38. — Citrus  mealy  bug  (Pseudococcus  citri  Risso).  The  two  figures  on 
the  right  show  the  development  of  the  cottony  mass  in  which  the  eggs  are 
deposited. 

seeming  to  delight  particularly  in  the  fruit.     Masses  of  the  insect  with 
eggs  and  young  may  cluster  on  the  fruit,  and  in  the  case  of  the  navel 


Fig.    39. — Mealy  bug  on  oranges. 

orange,  will  be  sure  to  be  found  secreted  in  the  navel  end.  It  also  gives 
off  a  very  sticky  sort  of  honeydew  that  makes  it  exceedingly  difficult  to 
wash  the  fruit  clean,  in  addition  to  getting  the  insects  themselves 
removed.     Hidden  in  the  navel  of  the  orange,  they  may  pass  through 


Bulletin  214] 


CITRUS   FRUIT    INSECTS. 


483 


the  washing  machine  and  also  the  hand  cleaning.  This  also  happens  on 
the  lemon,  and  when  this  fruit  is  left  in  the  packing  house  for  curing, 
they  may  continue  to  breed  undisturbed.  On  account  of  its  habit  of 
seeking  protected  places,  they  congregate  at  the  base  of  the  petiole  of  the 
leaf  or  stem  of  the  fruit  causing  the  leaves  and  young  fruit  to  drop 
prematurely.  Because  of  the  injury  to  the  fruit,  from  the  attacks  of  the 
insects  themselves,  and  also  through  the  vigorous  washing  and  cleaning, 
the  loss  through  decay  in  transit  is  often  very  heavy. 


Fig.   40. — Mealy  bug  on  lemons. 


LIFE  HISTORY  AND  HABITS  OF  THE  MEALY  BUG. 

The  eggs  of  this  insect  are  laid  in  a  cottony  mass  which  is  secreted 
by  the  mature  female  as  the  eggs  are  deposited.  The  number  laid  by  a 
single  individual  will  be  from  350  to  400,  and  they  require  about  eight 
to  ten  days  to  hatch  during  the  warmer  months  and  in  winter  from 
fourteen  to  eighteen  days. 

The  young  move  about  more  or  less  throughout  their  development. 
They  may  not,  of  course,  migrate  very  far,  for  they  are  usually  busy 
feeding.  The  time  of  development  of  the  mealy  bugs  varies  consid- 
erably, taking  2\  months  from  March  to  May  and  about  1^  months 
during  the  summer.  Males  have  completed  their  life  cycle  in  two 
months  in  winter  and  only  about  one  month  during  the  warmer  weather 
of  summer.     The  females  appear  to  have  the  habit  of  producing  eggs 


484  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

before  they  attain  full  size,  in  which  cases  they  continue  to  enlarge  as 
the  eggs  are  deposited. 

NATURAL  ENEMIES  OF  THE  MEALY  BUG. 

The  mealy  bug  being  a  soft-bodied  insect  and  exposed  as  it  is  on  the 
tree,  is  subject  to  the  attacks  of  a  considerable  number  of  parasites  and 

predaceous  insects.  Space  will  not 
permit  of  a  full  discussion  of  these 
here.  There  are  several  different 
species  of  ladybird  beetles  that  prey 
upon  them,  and  the  one  that  is  to  us 
best  known,  and  probably  the  most 
important,  is  Cryptolaemus  mon- 
fig.  4i.-Hemerobius  larva.  trouzieri.     The  larvae  of  this  beetle 

are  covered  with  cottony  tufts,  and  as  they  occur  among  the  masses  of 
the  mealy  bug,  are  not  readily  distinguished  from  them.  The  beetle 
itself  is  black  in  color  and  tipped  with  yellowish  brown  at  either  end. 
The  under  side  is  light  brown,  excepting  where  the  legs  arise,  which  is 
black. 

Beside  the  ladybird  beetles  there  are  the  lacewing  Hemerobius  and 
Syrphus  fly  larvae,  and  several  internal  parasites  that  attack  the  mealy 
bug.  Professor  R.  W.  Doane,  who  assisted  in  this  investigation  during 
the  summer  of  1910,  has  observed  one  Hemerobius  larva  eat  16  partly- 
grown  mealy  bugs  in  an  afternoon. 

CONTROL  OF   THE   MEALY   BUG. 

This  insect  is  one  of  the  most  difficult  of  all  the  pests  to  actually 
kill  all  of  its  numbers.  It  is  very  or  quite  resistant  to  fumigation 
dosages  as  ordinarily  used  on  citrus  trees,  and  because  of  its  habit  of 
congregating  in  masses  or  hidden  away  in  the  navel  of  the  orange  or 
other  secluded  places,  it  is  impossible  to  reach  or  kill  them  all  with  a 
spray.  But  of  the  two  methods,  the  experience  in  San  Diego  County 
and  also  more  recently  in  Ventura,  is  that  the  spray  is  more  effective 
than  fumigation.  The  spray  that  Mr.  Essig,  Horticultural  Commis- 
sioner of  Ventura  County,  especially  recommends  is  the  carbolic  acid 
emulsion,  consisting  of  1  gallon  of  crude  carbolic  acid  and  8  pounds  of 
whale-oil  soap  to  170  gallons  of  water.  The  soap  and  carbolic  acid  are 
dissolved  in  hot  water.  Kerosene  emulsion,  or  the  kerosene  water  spray, 
discussed  at  the  close  of  this  bulletin,  will  also  give  fairly  satisfactory 
results.  But  with  bad  infestations  two  or  three  sprayings  should  be 
made  at  intervals  of  three  or  four  weeks. 


Bulletin  214] 


CITRUS   FRUIT    INSECTS. 


485 


RED  SPIDERS. 

{Tetranychus  mytilaspidis  Riley.) 
(Tetranychus  sexmaculatus  Riley.) 

The  species  named  above  are  the  two  common  species  of  red  spiders 
attacking  citrus  trees  in  the  State.  They  occur  all  over  the  citrus  belt 
and  in  one  place  or  another  do  considerable  injury  each  year.  In  the 
early  spring  is  when  they  become  most  abundant  and  do  most  damage. 
Later  in  the  spring  or  summer  they  largely  disappear,  although  they 
may  be  found  on  the  trees  the  year  around. 

The  injury  caused  by  the  red  spiders  is  due  to  the  consuming  of  the 
plant  juices,  as  indicated  by  the  pale  spots  where  their  mouth  parts  are 


Fig.  42. — The  Florida  Red  Spider.     xl40. 

inserted.  This  gives  a  mottled  effect  to  the  leaf,  and  later  assumes  an 
ashy  gray  or  yellowish  appearance  with  but  little  chlorophyll  or  green 
matter  left.  Leaves  thus  affected  later  fall  from  the  tree.  The  same 
effect  is  produced  on  the  fruit  as  regards  the  grayish  or  silvery  appear- 
ance of  the  rind.  Another  phase  of  injury  that  has  become  important 
in  some  packing  houses  during  the  past  year  is  the  breeding  of  the 
spiders  and  consequent  injury  to  lemons  during  the  curing  process. 

Both  species  of  red  spiders  have  come  into  the  State  from  Florida. 
These  are  commonly  distinguished  by  the  differences  in  color  and  mark- 
ings. T.  mytilaspidis,  or  the  Florida  red  spider,  is  distinctly  red  in 
color,  while  T.  sexmaculatus,  or  the  six-spotted  mite,  is  pale  gray  in 
color  with  six  dark  spots.  The  former  does  the  more  injury  of  the  two, 
and  is  more  generally  distributed.  In  addition  to  the  differences  in  the 
mites  themselves,  their  habits  of  feeding  are  different.  The  Florida  red 
spider  feeds  generally  over  the  entire  surface  of  the  leaf  or  fruit  making 
a  uniform  mottled  effect,  whereas  the  six-spotted  species  feeds  largely 


486  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

on  the  under  side  of  the  leaf  and  is  confined  to  restricted  areas.  These 
are  usually  along  the  mid  rib,  and  extend  outward  and  forward  in  the 
direction  of  the  cross  veins.  These  spots  are  pale  colored  with  old  cast 
skins  and  black  specks  on  the  surface,  and  covered  usually  with  a  web. 
On  the  upper  surface  the  leaf  is  swollen  upward,  corresponding  to  the 
depression  on  the  lower  surface,  and  the  area  is  smooth  and  pale  yellow- 
ish in  color. 

LIFE  HISTORY  AND  HABITS  OF  THE  RED  SPIDER. 

What  follows  on  the  life  history  has  been  worked  out  for  T.  mytilas- 
pidis,  but  the  other  species  is  probably  very  similar. 

The  eggs  are  minute,  nearly-spherical,  red  bodies,  occurring  singly 


Fig.  43. — Orange  leaf  with  area  in  center  showing  work  of  the  Florida 

Red  Spider. 

on  the  leaf  and  held  in  place  by  an  upward  projecting  stalk  with 
radiating  guy  threads  extending  down  to  the  leaf.  They  require  ten 
days  to  hatch  during  May,  when  they  are  most  abundant.  From  0  to 
6  or  7  eggs  will  be  deposited  each  day. after  egg  laying  begins.  This 
will  continue  for  about  four  weeks,  and  the  average  number  laid  each 
day  will  be  2  or  3.  Many  of  the  spiders  do  not  lay  for  the  full  period 
so  that  the  number  of  eggs  deposited  will  range  from  30  to  75. 

The  young  mite  at  once  begins  to  feed  and  comes  to  maturity  in 
twelve  days,  during  which  time  it  has  molted  three  times  at  intervals 
of  three  days  each.  The  young  mite  as  it  hatches  from  the  egg  has 
but  six  legs,  but  during  the  first  molt  it  acquires  another  pair,  making 
eight,  which  is  the  usual  number  for  most  spiders  and  mites.  In 
twelve  days  to  two  weeks  they  are  depositing  eggs,  which  is  continued 
for  a  month  longer.  The  entire  life  cycle,  therefore,  will  be  about  forty 
days,  allowing  ten  days  for  the  eggs  to  hatch,  twelve  days  for  the  devel- 
opment of  the  young  and  four  weeks  for  adult  life.  Male  spiders, 
which  are  smaller  in  size  than  the  females,  are  usually  present,  but  we 


Bulletin  214 J  CITRUS  FRUIT  INSECTS.  487 

have  determined  that  eggs  may  be  produced  and  young  hatched  without 
them. 


Fig.  44. — Orange  leaf  on  right  showing  characteristic  feeding  areas  of  six- 
spotted  mite  on  lower  surface.     On  left,  upper  surface  of  same  leaf. 

CONTROL   OF   RED   SPIDERS. 

The  standard  remedy  for  spiders  and  mites  is  sulfur.  It  is  usually 
applied  dry,  dusted  over  the  tree.  This  may  be  done  by  hand,  but 
better  by  a  rotary  bellows.  In  procuring  the  sulfur,  fineness  is  the 
most  important  consideration.  The  vapor  of  sulfur  is  effective  but  for 
a  very  short  distance,  a  fraction  of  an  inch,  so  that  evenness  of  distribu- 
tion, instead  of  large  amounts  here  and  there,  is  more  efficient  and  less 
wasteful  of  the  sulfur.  There  is  no  stated  time  for  application.  It 
should  be  applied  just  as  soon  as  injury  by  the  spiders  is  apparent. 
This  will  be  some  time  in  the  early  spring.     A  temperature  of  about  75° 

4— b214 


488 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


is  necessary  to  properly  vaporize  the  sulfur.  The  higher  the  temper- 
ature above  this,  the  more  quickly  the  sulfur  acts.  Select,  therefore, 
days  that  will  have  a  bright,  warm  sun  in  the  middle  of  the  day,  but 


mm/7   /  J 

lH.         «  1^       ^»                ./' - 

1             .  -'       .    ' 

\ 

y*^&F 

Fig.  45. — Tip  of  orange  twig  showing  work  of  six-spotted  mite  on  the  leaves. 


apply  the  sulfur  in  the  early  morning  while  the  dew  is  still  on  the 
foliage.  If  a  sulfur  spray  is  desired,  use  30  pounds  of  sulfur  and  15 
pounds  of  lime,  as  milk  of  lime,  to  200  gallons  of  water,  or  1  to  35  or  50 
parts  of  the  commercial  lime  sulfur. 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  489 

THE  SILVER  MITE. 

(Eriophyes  oleivorus  Ash.) 

The  silver  mite  in  California  is  restricted  to  a  comparatively  small 
section  in  San  Diego  County.  This,  again,  is  an  imported  pest,  having 
come  into  the  State  from  Florida  in  1889.  The  once  familiar  russet 
orange  of  Florida  was  the  result  of  the  work  of  this  mite  on  the  rind. 
This  mite  attacks  both  the  foliage  and  the  fruit,  but,  of  course,  the 
most  injury  is  done  to  the  fruit.     The  green  lemon  takes  on  a  decidedly 


Pig.  46. — Lemon  on  right  showing  work  of  silver  mite. 

silvery  appearance,  which  is  due  to  the  extraction  of  the  oils  and  green 
matter,  or  chlorophyll.  On  account  of  this  silvery  effect  on  the  lemon, 
which  is  the  principal  variety  of  citrus  grown  in  the  section,  it  is  known 
here  as  the  silver  mite.  In  Florida  it  is  called  the  rust  mite  of  the 
orange.  If  the  lemons  are  allowed  to  ripen  on  the  tree  they  take  on 
this  russet  effect,  but  not  to  such  a  marked  extent  as  is  the  case  with 
the  orange. 

LIFE   HISTORY   AND   HABITS   OF   THE   SILVER   MITE. 

The  eggs  are  somewhat  like  the  red  spider  eggs,  excepting  that  they 
are  pale  yellow  in  color  and  smaller.  They  are  laid  singly  or  in  small 
clusters  on  the  foliage  or  fruit,  and  hatch  in  four  or  five  days  in  summer 
and  ten  to  fourteen  days  in  winter.  The  young  mite  soon  begins  to 
feed,  and  after  about  a  week  sheds  its  skin,  which  brings  it  to  the  adult 


490 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


form.     A  couple  of  weeks  are  all  that  are  necessary,  therefore,  to  bring 

it  from  the  egg  to  maturity.     This 

will  be  the  period  for  the  warmer   y^      nlulW^' 

weather,  and  in  colder  weather  this   jiff     IffijlilUa. 

will  be  doubled.     The   adult  mite, 

Fig.  47,  looks  very  different  from 

its  near  ally,  the  red  spider.     It  is  FlG-  ^.-snver  Mite. 

more  worm-like  and  has  but  four  legs,  while  the  red  spider  has  eight. 

THE   CONTROL  OF  THE  SILVER  MITE. 

Same  as  for  red  spiders,  page  487. 

THRIPS. 

Most  orange  or  lemon  growers  are  familiar  with  the  fact  that  upon 
shaking  the  blossoms  into  the  hand,  there  will  be  likely  to  be  seen 


Fig.  48. — Work  of  thrips  (Euthrips  citri)  on  fruit. 

small  yellowish  to  black  insects  running  about.     These  are  thrips  of 
which  some  species  are  limited  almost  entirely  to  the  blossoms,  while 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


491 


others  attack  the  leaves  and  fruit  and  do  serious  damage.  The  orange 
thrips  (Euthrips  citri  Moul.)  causes  a  leathery,  distorted  growth,  and 
gives  a  pale  silvery  color  to  the  leaves.  On  the  fruit  they  often  work 
around  the  stem  making  a  very  distinct  ring,  as  shown  in  Fig.  48,  some- 
times also  working  down  in  streaks,  as  in  Fig.  48.  Later,  they  attack 
the  blossom  end  where  the  line  of  injury  is  not  so  distinctly  and  abruptly 
marked  off.  This  injury  to  the  fruit,  while  not  affecting  its  edible 
qualities,  decidedly  lowers  its  market  value,  and  such  fruit  must  be 
consigned  as  an  inferior  grade.  The  part  of  the  tree  attacked  is  the 
tender  growth,  and,  with  a  severe  infestation,  the  growth  of  the  tree  is 
considerably  interfered  with. 

The  foregoing  account  of  thrips  injury  is  due  to  the  citri  species  or 
regular  orange  thrips.     This  species  occurs  in  greatest  abundance  in 


Fig.  49. — Characteristic  rings  at  stem  end  of  small  oranges  made  by  thrips 

(Euthrips  citri). 

the  San  Joaquin  citrus  section.  It  also  occurs  in  southern  California, 
and  occasionally  does  some  injury  in  the  Redlands  district  and  more 
rarely  in  the  other  parts  of  the  citrus  belt.  Its  occurrence  at  Redlands 
may  be  due  to  the  fact  that  the  climate  there  is  more  nearly  like  that 
of  Tulare  County.  The  same  species  also  occurs  in  Arizona  and  does 
considerable  injury  there.  However,  the  only  place  where  it  is  serious 
enough  thus  far  to  warrant  inaugurating  control  measures  is  in  the 
San  Joaquin  belt  where,  during  the  past  year,  about  2,000  acres  of 
orange  trees  were  sprayed. 

Another  species  (Heliothrips  hcemorrhoidalis)  has  been  observed 
to  do  even  more  serious  injury  than  the  citri  species  on  a  few  trees. 
In  Santa  Barbara  County  three  or  four  cases  of  a  few  trees  each  were 
seen  to  have  practically  the  entire  foliage  and  also  the  fruit  severely 


492 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


affected  by  this  species.  The  leaves  were  of  a  mottled  pale  color  and 
many  had  yellowed  and  dropped  off,  and  the  entire  surface  of  the  fruit 
has  a  pale  silvery  color,  as  shown  in  Fig.  50.     This  species  has  also  been 


Fig.  50. — Orange  on  right  showing  work  of  thrips 
(Heliothrips  hsemorrhoidalis). 

taken  on  oranges  in  Kern-  County,  but  we  have  no  report  of  damage 
from  that  section. 

The  species  commonly  occurring  in  the  blossoms  of  citrus  trees  are 


Fig.  51. — Work  of  thrips  (H.  hsemorrhoidalis)   on  orange  leaf. 

Euthrips  tritici  Fitch  and  Euthrips  occidentalis.  These  are  common 
species  widely  distributed  over  the  State  and  attacking  various  kinds 
of  plants.  Thus  far  these  have  done  no  very  serious  injury  to  the  fruit 
or  foliage  of  the  orange  tree.     They  occur  in  the  blossoms   for  the 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  493 

purpose  of  feeding  on  flower  parts,  and  where  their  numbers  are  large, 
as  is  often  the  case,  they  probably  do  some  injury  to  the  flower  and 
consequent  setting  of  the  fruit.  But  this  injury  may  never  become 
serious  enough  to  warrant  any  attempt  at  control.  The  few  trees 
that  were  attacked  so  severely  by  the  hcemorrhoidalis  in  Santa  Barbara 
County  would  certainly  warrant  spraying.  But  the  most  widespread 
injury  is  done  by  E.  citri  and  the  discussion  below  on  control  has  special 
reference  to  this  species. 

A  certain  brown  spot  that  is  commonly  found  on  oranges  was  sup- 
posed to  be  due  to  thrips,  according  to  a  theory  that  was  promulgated 
several  years  ago.  Just  what  is  the  cause  of  such  spots  is  not  yet 
known,  but  thus  far  no  evidence  has  been  adduced  to  prove  that  it  is 
due  to  thrips,  and  it  is  certainly  not  characteristic  thrips  injury. 

LIFE  HISTORY  AND  HABITS  OF  THE  ORANGE  THRIPS. 

Adults  of  this  species  appear  in  the  early  spring  and  there  is  a  suc- 
cession of  broods  on  to  November.  In  1910,  they  first  made  their 
appearance  in  the  Lindsay  section  about  April  15th.  By  April  22d 
they  were  found  commonly  feeding  upon  the  more  tender  leaves. 

According  to  Mr.  J.  R.  Horton  of  the  Bureau  of  Entomology,  Wash- 
ington, who  has  been  investigating  this  species,  the  period  of  develop- 
ment is  from  seventeen  to  twenty-three  days  and  the  average  life  of  the 
adult  about  twenty-five  days.  He  has  also  determined  that  pupation 
does  not  occur  in  ground,  like  its  ally  the  pear  thrips,  but  in  rubbish, 
old  leaves,  blossoms,  and  under  bands,  in  the  case  of  trees  so  protected. 

CONTROL   OF   THRIPS. 

Spraying  seems  to  be  the  most  satisfactory  means  of  combating  the 
thrips  and  the  spray  that  has  been  recommended  by  the  Bureau  of 
Entomology  consists  of : 

Commercial  lime  sulfur    (33°) 2£  gals. 

Black  leaf  extract v 2  gals,  of  2|%,  or  14  fluid  oz.  of  40%. 

Water 200    gals. 

The  first  spraying  was  done  in  1910  on  April  25th,  and  it  is  necessary 

to  follow  this  with  a  couple  more  applications  at  intervals  of  about 

ten  days.     A  strong  pressure,  175  pounds,  is  necessary  to  reach  all  parts 

of  the  tree. 

APHIS. 

(Aphis  gossypii.) 

Often  in  the  early  spring  on  the  tender  shoots  of  citrus  trees  Aphids 
will  be  found  thickly  covering  the  twig  and  underside  of  the  leaves. 
The  result  of  their  injury  is  a  curling  of  the  leaves  and  a  checking  in 
growth  of  the  shoot.  Fortunately,  these  insects  never  completely 
infest  a  grove,  and  only  rarely  an  entire  tree.  Their  attack  is  confined 
to  a  few  shoots,  usually  so  that  the  effect  on  the  whole  tree  is  not  so 


494 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


serious.     Again,  they  disappear  very  suddenly  in  the  midst  of  a  maxi- 
mum infestation. 

Many   people   attribute  this   disappearance   entirely  to   a  Braconid 
parasite  which  attacks  them.    But  this  statement  is  not  always  based  on 

close  observation.  When  the  lice  disappear 
there  is  nothing  left  but  the  mummies  of  those 
which  have  been  parasitized.  The  conclusion 
is  that  they  have  all  been  thus  killed.  As  a  mat- 
ter of  fact,  where  there  is  one  mummy  left, 
there  were  often  a  score  or  more  of  lice  during 
the  infestation,  and,  since  it  is  only  the  mum- 
mies that  remain,  it  is  not  surprising  that  the 
parasite  should  have  all  the  credit.  Diseases 
and  weather  conditions  usually  must  be  consid- 
ered more  important  factors  in  the  control  of 
the  plant  lice  than  both  parasites  and  predaceous  enemies.  But,  how- 
ever, they  disappear,  the  important  thing  is  that  they  often  do  so,  and 
the  grower  is  relieved  of  the  necessity  of  inaugurating  control  measures. 
In  those  few  cases  where  they  are  present  and  do  much  injury,  they  may 
be  killed  by  a  nicotine  or  weak  soap  or  oil  spray.  In  the  case  of  budded 
trees,  where  there  is  much  tender  growth,  this  is  sometimes  advisable. 


Fig 


52. — Coccinella  abdom- 
inalis.  Sav,  feeding  on 
Aphids.     x5. 


THE  ORANGE  TORTRIX. 

(Tortrix  citrana  Pern.) 
Orange  growers  of  southern  California  have  been 

years  more  or  less  familiar 

with  the  work  of  a  worm 

burrowing   into   the   fruit. 

But   very   little   has    been 

known     about    the    insect 

itself  or  its  habits.     This 

insect  was  first  described  in 

1889  and  has  been  reported 

as  doing  injury  at  intervals 

since  that  time. 

During    the    season    of 

1909-10  it  was  the  cause  of 

considerable  concern  in  cer- 
tain sections  of  the  south- 
ern California  citrus  belt. 

It  was  most  abundant   in 

Los  Angeles  County,  from  fig.  53.— Eggs  of  orange 

Glendale  to  Covina.     In  some  of  the  packing  houses 


for  a  great  many 


tortrix.     xl4. 

during  the  early 


Bulletin  214] 


CITRUS   FRUIT    INSECTS. 


495 


part  of  the  season  the  wormy  fruit  amounted  to  between  5  and  10  per 
cent.  The  injury  is  due  to  the  burrows  made  in  the  fruit,  and  those 
usually  go  no  deeper  than  just  through  the  rind.  There  is  considerable 
variation  in  size  of  the  burrows,  as  shown  in  Fig.  56.  Fruit  that  is 
otherwise  sound  must  be  classed  as  culls  on  account  of  these  burrows, 
and  in  the  worst  infested  places  a  special  man  was  delegated  to  sort 
these  out  in  the  packing  house. 

Not  only  do  the  holes  themselves  mar  the  fruit,  but  these  are  the 
source  of  infection  for  several  kinds  of  decay,  including  the  blue  mold, 
the  navel  end  rot,  and  the  wither  tip  fungus.  An  orange  that  may 
show  no  outward  signs  other  than  the  worm  hole  may  be  badly  infected 
with  decay  in  the  interior.  Such  a  case  is  indicated  in  figures  57  and  58. 
The  burrows  in  the  fruit  also  often  cause  it  to  drop  prematurely, 
especially  if  the  fruit  is  still  small,  so  that  all  the  injury  by  this  insect 
is  not  accounted  for  in  the  packing  house  alone. 

This  insect  attacks  a  wide  range  of  food  plants  aside  from  the  orange. 
Among  those  may  be  mentioned  the  apricot,  willow,  oak,  wild  walnut, 
golden  rod,  and  a  large  number  of  greenhouse  plants.  On  these  plants 
the  larvae  feed  upon  the  leaves 
mostly,  and  these  are  matted 
together  by  means  of  silk 
threads  which  it  secretes.  In 
the  case  of  Pelargoniums, 
they  also  work  in  the  tip  and 
branches  similar  to  a  borer. 

LIFE    HISTORY    AND    HABITS    OF 
THE  ORANGE  TORTRIX 

The  eggs  are  laid  on  the 
leaves,  usually  the  lower  sur- 
face and  also  on  the  orange  it- 
self. These  are  laid  in  masses 
of  from  10  to  35,  and  overlap 
one  another  like  fish  scales. 
An  individual  egg  is  cream 
color,  3/100  of  an  inch  in  di- 
ameter, disc-shaped,  and  with 
distinctly  marked  hexagonal 
net  work.  Two  or  three  of 
these  masses  may  be  laid  by  a 

single  moth,  the  total  number  of  eggs  varying  from  30  to  75. 
occurs  in  twelve  days. 

The  young  larva  upon  hatching  feeds  upon  the  surface  of  the  fruit 
at  first  by  making  small  burrows,  but  later  confines  its  feeding  to  a 
single  burrow.     A  thin  network  of  silk  is  often  spun  about  the  entrance. 


Fig.  54. — Larva  and  adult  of  orange  tortrix 
(Tortrix  citrana  Fern.).  Larva  enlarged 
5  times.     Moth  about  lh  times  natural  size. 


Hatching 


496 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


Larva  in  the  insectary  entered  the  fruit  on  the  underside,  where  it  was 
resting  on  the  surface.  In  the  field  the  most  usual  place  of  entry  is 
where  two  oranges  are  in  contact  or  where  a  leaf  is  resting  upon  the 
fruit. 

The  full  grown  larva  is  about  half  an  inch  long  and  the  color  varies 
from  greenish  white  to 
dark  gray,  with  irregular 
stripes,  which  show  more 
distinctly  in  the  darker 
specimens.  During  the 
growing  period  the  worms 
remain  almost  continuous- 
ly within  the  fruit,  but 
upon  reaching  maturity 
they  may  emerge  and 
wander  about  seeking  a 
suitable  place  for  pupa- 
tion. If  such  a  place  is 
not  found  they  will  pu- 
pate within  their  burrow, 
in  fact,  this  a  very  com- 
mon place  chosen.     The  total  period  necessary  to  bring  the  larva  to 


Fig.  55. — Orange  tortrix.     Pupal  skin  in  burrow 
and  moth  which  emerged  from  it. 


Fig.  56. — Squares  of  orange  rind  showing  the  different  types  of  burrows 
made  by  the  orange  tortrix. 


maturity  is  from  fifty-five  to  sixty  days  and  the  pupal  period  lasts  from 
nine  to  twelve  days  in  midsummer. 

There  is  considerable  overlapping  of  broods  so  that  the  number  is 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


497 


not  very  well  defined.  But  there  is  a  period  in  the  spring,  when  the 
moths  are  abundant,  and  again  in  the  early  fall.  Moths  were  common 
in  May  and  the  first  part 
of  June,  and  practically 
none  seen  in  July  and 
August.  Judging  from  the 
appearance  of  the  worms 
and  of  the  moths  there  are 
probably  three  generations 
in  a  year,  in  the  orange 
groves.  It  has  not  been  un- 
common to  find  the  larva  of 
this  orange  worm  parasi- 
tized. Those  species  that 
have  been  reared  are  two 
new  species  of  Braconids, 
not  yet  described.  These, 
upon  completing  their  de- 
velopment, about  the  time 


Fig.    57. — Orange    showing   burrow    of    orange 
tortrix.     No  evidence  of  decay  on  outside. 


the  worm  is  full  grown, 
emerge  and  pupate  in  a 
cylindrical  silken  cocoon. 
As  for  artificial  control 
of  this  insect,  spraying 
with  an  arsenical  might 
be  feasible  if  they  became 
very  abundant,  but  it  is 
not  likely  that  this  will 
ever  be  necessary.  With 
the  present  status  of  in- 
jury the  most  practical 
measure  is  to  pick  up  and 
destroy  all  dropped  fruit 
in  the  field  while  the 
larva  is  still  within  its 
burrow,  and  also  the  de- 
struction of  the  wormy 
culls  as  they  are  sorted  in  the  packing  house.  This  is  a  case  where  an 
insect,  that  is  probably  native  and  accustomed  to  feed  upon  other  plants, 
has  adjusted  itself  to  new  conditions. 


Fig.  58. — Same  orange  as  shown  in  figure  57 
cut  into  showing  infection  as  result  of  the 
burrow  of  the  orange  tortrix. 


498 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


Fig.  59. — Oranges  showing  two  stages  of  decay  induced  through  the  burrows 
of  the  orange  tortrix.     Burrows  shown  in  center  of  areas. 


Fig.  60. — Burrows  in  fruit  and  leaf  folded  by 
Amorbia  emigratella,  Busch,  a  Central  American 
insect  introduced  into  Hawaii  but  hitherto  not 
recorded  from  California. 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  499 


FULLER'S  ROSE  BEETLE. 

(Aramigus  fulleri  Horn.) 

This  is  a  grayish  brown  beetle  that  measures  something  more  than  a 
quarter  of  an  inch  long.  It  tapers  toward  the  head,  which  ends  in  a 
short  snout.  The  grayish-brown  coloring  is  due  to  scales  which  cover 
the  body.  These  beetles  may  be  seen  clinging  to  a  twig,  the  underside 
of  a  leaf,  or  at  some  fork  among  the  smaller  branches. 
They  are  nocturnal,  and  have  the  habit  of  feeding  at 
night,  while  during  the  day  remain  quiet  and  avoid 
the  light  as  much  as  possible. 

The  characteristic  injury  of  the  beetles  on  orange 
leaves  is  shown  in  figure  62.  On  large  trees  they  feed 
mostly  in  the  lower  and  interior  part  of  the  tree,  this 
being  due  partly  to  their  light-shunning  habits.  But 
it  is  on  newly  budded  trees  that  this  insect  does  the 
severest  injury.  They  especially  delight  in  the  tender  FiG  61_Fuller-s 
leaves  and  often  destroy  most  of  the  foliage.  rose  *>eetle-    x4- 

LIFE    HISTORY   AND   HABITS  OF   THE   ROSE   BEETLE. 

The  eggs  are  laid  in  batches  of  from  10  to  50,  usually  in  some  scar 
on  the  bark  of  the  tree.  These  require  three  or  four  wreeks  to  hatch. 
The  larva  crawls  down  to  the  ground  and  feeds  on  the  roots  of  the  tree. 
Usually  more  injury  is  done,  though  not  often  appreciated,  to  the  roots 
by  the  larva  of  this  insect  than  is  done  by  the  beetle  on  the  foliage. 


The  fact  that  the  adult  beetle  is  unable  to  fly  and  is  dependent  upon 
crawling  alone  for  the  ascent  of  the  tree,  makes  it  easy  to  prevent  their 
attack  on  the  foliage.  The  method  most  popular  with  orange  growers 
is  to  band  the  tree  trunk  with  cotton.  A  band  of  this  about  4  inches 
wide  is  placed  about  the  tree  and  tied  by  means  of  a  string  on  the  lower 
side  of  the  band.  The  band  is  then  pulled  down  over  the  string  so 
that  it  extends  out  a  short  distance  from  the  trunk.  Tree  tangle-foot 
makes  another  excellent  barrier. 


500 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


Fig.  62. — Work  of  Fuller's  rose  beetle  on  orange  leaves. 


Fig.  63. — Small  orange  trees  banded  with  cotton  for  protection  against 
Fuller's  rose  beetle. 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


501 


Fig.  64. — Work  of  white  ants  in  orange  wood. 


DIABROTICA  SOROR. 

This  is  the  familiar  green  beetle  with  twelve  black  spots  that  is  to  be 
seen  everywhere  and  on  all  sorts  of  plants.  It  often  does  much  damage 
to  the  tender,  growing  shoots  of  the  orange.  The  lemon  foliage  is 
but  rarely  attacked.  In  a  grove  where  orange  and  lemon  trees  were 
planted  alternately,  it  was  ob- 
served that  no  noticeable  in- 
jury occurred  on  the  lemon, 
while  all  the  young  growth  of 
the  orange  was  severely  at- 
tacked. In  the  case  of  budded 
trees,  they  are  specially  likely 
to  suffer  from  the  attacks  of 

Diabrotica.    The  larva  is  sub-  «ffi?.y</  ^-   ^^v,         >&, 

terranean  and  feeds  on  several  *    "?   *  ^7  ^ 

different  kinds  of  plants. 

CONTROL  OF  DIABROTICA. 

There  are  two  methods  of 
handling  diabrotica,  namely, 
jarring  and  poisoning.  If  the 
trees  are  small  the  beetles  may 
be  jarred  off  on  a  tarred  or 
oiled  screen  in  the  early  morn- 
ing while  they  are  still  slug- 
gish. Or  the  tender  growth,  where  the  feeding  occurs,  may  be  sprayed 
with  arsenate  of  lead,  8  pounds  to  200  gallons  of  water,  or  1J  pounds 
paris  green  to  200  gallons  of  water. 


Diabrotica  soror. 


502  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


Fig.    66. — Work  of  Diabrotica  soror  on   orange   leaves. 


Fig.  67. — Paper  sacks  on  recently  budded  orange  trees  for  protection  against 
Diabrotica.     Negative  by  J.  E.  Coit. 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


503 


SERIOUS  CITRUS  FRUIT  PESTS  NOT  YET  ESTABLISHED  IN  CALIFORNIA. 

The  reader  will  have  noticed  that  in  the  discussions  of  the  various 
pests  in  this  bulletin,  that  all  the  important  ones,  without  exception, 
have  been  imported  into  this  State.  We  have  with  us,  therefore,  prac- 
tically all  the  serious  citrus  fruit  pests  excepting  the  orange  maggot 
and  the  white  fly;  and  even  the  latter  got  fairly  well  established  in 
the  upper  Sacramento  valley  a  few  years  ago.  A  few  additional  scale 
insects  might  still  be  imported,  but  it  is  probable  that  none  of  these 
would  rank  in  importance  with  those  that  are  already  here,  and  on 
account  of  the  universal  practice  of  fumigation,  these  would  be  con- 
trolled along  with  the  others.  But  such  insects  as  the  white  fly,  the 
orange  maggot,  and  other  fruit  flies  would  probably  necessitate  the 
inauguration  of  additional  control  measures  that  would  greatly  increase 
our  already  heavy  tax  for  insect  protection. 


Fig.  68. — Larva  of  orange 
maggot.     x4. 


THE  ORANGE  MAGGOT. 

{Trypeta  ludens  Loew.) 
This  is  an  insect  that  is  a  serious  pest  of  oranges  in  Mexico.  The 
larva  or  maggot  develops  within  the  fruit  similar  to  the  codling  moth 
within  the  apple.  From  4  or  5  to  15  or  20  of  these  maggots  may  occur 
in  a  single  orange.  The  eggs  from  which  these  maggots  hatch  are 
deposited  on  the  fruit.  About  70  eggs  ^tftyfifffiW^ 
are  laid  by  a  single  fly,  and  these  are  -^ 
distributed  over  from  eight  to  a  dozen 
oranges.  When  the  worm  has  attained 
its  growth  it  leaves  the  fruit,  which  usually  falls.  In  case  it  does  not 
fall,  the  maggots  drop  to  the  ground.  The  complete  life  cycle  requires 
about  three  months. 

APPEARANCE   OF   THE   ORANGE    MAGGOT. 

From  our  point  of  view  it  is  most  important  to  know  what  the  insect 
looks  like,  especially 
the  maggot  so  that  in 
case  it  appears,  there 
will  be  no  delay  in 
reporting  its  presence. 

The  larva  or  mag- 
got is  dirty  white  in 
color   and   when   ma- 


Fig.    6  ». —  Pupa   of  orange 
maggot.     x4. 

5— b214 


Fig.  70. — Fly  of  orange  maggot  (Trypeta  ludens.     x3. 


504 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


ture  measures  slightly  less  than  one  half  of  an  inch  long.  This  is  the 
stage  of  the  insect  that  occurs  in  the  pulp  of  the  orange.  The  pupa- 
rium  which  is  the  next  stage  is  light  brown  in  color,  barrel-shaped  and 
measures  about  one  third  of  an  inch  long.  The  adult  fly  is  straw  yellow 
in  general  color  with  brownish  markings  on  the  wings,  which  when 
spread  measure  about  five  sixths  of  an  inch  across. 


THE  CITRUS  WHITE  FLY. 

(Aleurodes  citri  R.  &  H.) 

The  citrus  white  fly  is  one  of  the  most  important  pests  of  citrus  fruits 
in  Florida.  There  it  outranks  all  the  scale  insects 
as  a  pest  and  is  less  amenable  to  treatment.  It  was 
formerly  held  that  an  insect  that  thrives  so  well  in 
a  humid  climate  like  that  of  Florida  would  not  be 
likely  to  become  an  important  pest  in  our  arid  Cali- 
fornia climate.  But  such  a  claim  can  be  no  longer 
held,  since  the  white  fly  got  a  foothold  two  or  three 
years  ago  in  certain  points  in  the  Sacramento 
valley.  This,  too,  in  a  section  that  has  the  typical 
dry,  hot,  interior  climate. 


Fig.    71. — Larva    of 
white  fly.     xl8. 


The  nature  of  injury  of  the 
white  fly  is  similar  to  that  of 
the  black,  soft  brown,  and 
other  unarmored  scales;  that 
is,  it  is  not  so  much  the  life  of 


Fig.   72. — Cast  skin  of  white  fly. 


Fig.  73. — Adult  of  white  fly.     xl5. 


the  tree  that  is  threatened,  as  the  injury  consequent  to  the  honeydew 
and  sooty  mold.  Leaves  of  trees  infested  with  white  fly  may  be  com- 
pletely covered  with  the  insects  themselves  on  the  under  side,  together 


Bulletin  214] 


CITRUS   FRUIT   INSECTS. 


505 


with  the  sooty  mold  on  the  upper  side,  and  thus  the  natural  functions  of 
the  leaves  are  impaired,  and  fruit  from  such  trees  is  tasteless  and  insipid. 
The  larva  of  the  white  fly  is  shown  in  figure  71.  It  is  ovel  in  shape, 
slightly  less  than  one  sixteenth  of  an  inch  long,  of  a  pale  greenish 
yellow  color  and  lies 
very  flat  upon  the  leaf. 
The  adult  is  a  small  fly 
measuring  about  one 
tenth  of  an  inch  long 
and  covered  with  a  fine 
white  powder,  hence 
the  name  white  fly. 


SPRAYING  TOR  CITRUS 
FRUIT  INSECTS. 

Spraying  which  is 
the  main  reliance  for 
the  control  of  most  in- 
sects of  deciduous  trees 
has  never  been  quite 
satisfactory  with  the 
citrus  tree.  On  ac- 
count of  the  dense  foli- 
age of  the  citrus  tree  it 
is  very  difficult  to  reach 
all  its  parts,  and  since 
there  is  no  dormant 
period,  the  application 
of  insecticides  suffi- 
ciently strong  to  kill 
.  all  stages  of  the  insects 
is  not  permissible. 
Formerly,  spraying  in 
the  citrus  belt  was 
more  widely  practiced 
than  at  present.  Spray- 
ing   has    lost    ground 

Chiefly    for    the    reason  FlG-   74.— Leaf  infested  with  white  fly. 

that  growers  have  come  to  more  generally  believe  in  the  better  efficiency 
of  fumigation.  Spraying  came  into  ill-repute  also  through  the  injury 
due  to  the  old  distillate  spray,  which  not  only  spotted  the  fruit,  but 
dropped  the  leaves  in  many  cases. 


506  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

In  spite  of  the  fact  that,  as  a  general  practice  nnder  all  conditions, 
spraying  is  out  of  the  question,  it  still  has  a  limited  place  in  the  control 
of  citrus  scales.  Eighteen  thousand  dollars  is  expended  annually  for 
spraying  citrus  trees  in  Riverside  and  San  Bernardino  counties.  If 
there  is  a  uniform  hatch  of  black  scale,  and  they  are  all  small,  there  is 
no  doubt  but  that  a  thorough  spraying  will  keep  them  in  check.  But  in 
the  case  of  the  purple  scale,  with  eggs  always  likely  to  be  present,  very 
poor  results  may  be  expected.  The  principal  field  for  spraying  is  in  the 
case  of  young  trees  infested  with  the  black  scale  or  a  few  trees  about  the 
dooryard,  where  it  is  often  difficult  to  get  the  work  done  by  fumigation. 

The  objection  formerly  held  in  regard  to  the  injury  to  the  tree  and 
fruit  no  longer  occurs  with  the  lighter  grade  of  oil  used.  The  distillate 
was  a  28°  gravity  oil,  and  was  used  at  a  strength  of  2  per  cent.  The  oil 
that  is  now  in  most  general  use  is  a  cheap  grade  of  ordinary  kerosene. 
This  is  used  at  a  strength  of  10  per  cent,  the  formula  being  as  follows : 

Kerosene  or  water  white  oil 20  gallons 

Water    200  gallons 

This  is  applied  only  with  a  power  outfit  with  a  good  agitator  which 
is  necessary  to  make  a  mechanical  mixture  of  the  oil  and  water.  Where 
there  are  but  a  few  small  trees,  and  a  hand  outfit  is  to  be  used,  kerosene 
emulsion  may  be  substituted.     The  formula  is  as  follows : 

Kerosene 1  gallon 

Soap    -J  pound 

Water    15-  gallons 

Dissolve  soap  in  a  gallon  of  hot  water,  add  1  gallon  of  kerosene,  and 
mix  by  turning  nozzle  of  spray  pump  back  into  mixture,  and  then  dilute 
to  make  15  gallons. 


FUMIGATION. 

It  is  not  intended  in  this  general  bulletin  to  discuss  all  the  phases  of 
the  subject  of  fumigation,  but  simply  to  give  a  few  of  the  more  impor- 
tant facts.  Those  wishing  a  more  detailed  treatment  of  the  subject 
should  send  to  the  State  Experiment  Station  for  Circulars  11  and  50 
by  Prof.  C.  W.  Woodworth,  and  to  the  Bureau  of  Entomology,  Wash- 
ington, for  Bulletins  79  and  90  by  Mr.  R.  S.  Woglum. 

VARIATION  OF  DOSAGE. 

Seven  or  eight  years  ago  the  experiment  station  had  a  man  in  the  field 
for  the  purpose  of  determining  the  actual  practice  of  scheduling  dosage. 
Practically  all  of  the  fumigating  outfits  then  operating  in  the  State 
were  visited,  and  the  tented  trees  accurately  measured  and  the  doses 
given  them  by  the  scheduler  recorded.     Thus,  the  dosage  and  measure- 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  507 

ments  of  over  2,000  trees  were  made,  representing  the  actual  practice  of 
30  fumigators. 

From  this  study  it  was  found  that  for  a  10-foot  tree,  having  the  two 
dimensions  approximately  equal,  the  dosage  varied  from  2  to  7J  ounces. 
And  for  a  20-foot  tree  the  variation  was  from  7  to  32  ounces.  This  is 
evidence  enough,  without  further  comment,  in  favor  of  some  system  of 
measurement  or  accurate  calculation  of  dosage  as  against  the  old  system 
of  guessing. 

FACTORS  IN  VARIATION  OF  DOSAGE. 

There  are  three  principal  factors  that  account  for  the  great  variation 
in  dosage :  first,  there  is  the  inaccuracy  of  judging  the  exact  size  of  the 
tree,  and  the  consequent  dosage ;  second,  there  is  the  difference  of  opinion 
of  different  fumigators  as  to  the  dose  a  particular  sized  tree  infested 
with  a  particular  scale  should  have.  For  example,  a  tree  infested  with 
red  scale  that  measures  20  feet  over  the  top  and  30  feet  around  the  base ; 
one  man  will  say  it  should  have  4  ounces,  another  5,  another  6,  and 
another  8.  Thus,  there  may  be  a  variation  of  50  per  cent  for  the  same 
tree  and  infested  with  the  same  insect;  third,  there  is  the  variation  in 
dose  as  the  size  of  the  tree  varies.  We  will  assume  that  all  fumigators 
agree  on,  say  four  ounces  as  the  proper  dose  for  a  tree  20  by  30  feet. 
Then,  for  a  tree  twice  that  size,  the  same  people  will  vary  their  dose 
from  10  to  30  ounces.  This  is  a  difference  in  basis  of  calculation  or 
variation,  as  the  size  of  the  tree  increases  or  diminishes. 

The  first  two  of  these  factors  are  easily  remedied.  The  exact  size  of 
the  tree  can  be  ascertained  by  some  system  of  measurement ;  and  there 
should  be  a  general  agreement  as  to  how  much  cyanide  is  necessary  to 
kill  the  different  scales.  But  the  third  factor,  namely,  varying  the 
dosage  properly  according  to  the  size  of  the  tree,  is  a  more  difficult  and 
complicated  question. 

BASIS  FOR  DOSAGE. 

The  first  dosage  schedule  published  was  based  upon  the  cubic  contents. 
This,  naturally,  would  be  the  logical  basis  for  calculation ;  but  in  actual 
practice  it  was  soon  found  that  a  large  tree  required  a  dose  proportion- 
ally less  than  a  smaller  tree.  This  is  accounted  for  through  the  leakage 
of  gas,  and  a  small  tree  has  more  tent  surface  per  unit  of  volume  than  a 
larger  tree.  So  many  widely  different  schedules  were  proposed  until 
finally  actual  field  practice  established  a  more  or  less  elastic  schedule 
with  the  approximate  proper  variation  in  dosage  according  to  the  size 
of  the  tree. 

AREA  BASIS. 

This  has  worked  out  into  practically  an  area  basis  rather  than  a 
volume  basis,  that  is,  trees  receive  a  dose  more  nearly  according  to  the 


508  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

area  of  their  tent  surface  than  to  the  cubic  contents  of  the  tented  tree. 
This  basis  of  dosing  a  tree  according  to  the  tent  surface  was  proposed 
by  Woodworth  of  this  station  in  1903,  and  it  is  the  one  adopted  by  Mr. 
Woglum. 

SCHEDULES  AND  CALCULATION. 

The  following  is  a  very  simple  formula  by  means  of  which  any  one 
can  construct  his  own  schedule.  This  formula  is  simply  to  multiply  the 
circumference  of  the  tented  tree  by  the  distance  over  the  top  and  point 
off  two  places.  The  result  is  the  number  of  ounces  of  cyanide  for  the 
given  tree  for  the  purple  scale,  or  the  maximum  dosage : 

Examples:     A  tree  20x30 6  ounces  cyanide. 

30x40 12  ounces  cyanide. 

This  is  the  schedule  for  the  purple  scale  and  corresponds  in  general 
with  Mr.  "Woglum 's  schedule  No.  1.  For  the  red  and  yellow  scales,  or 
for  the  black  scale,  excepting  where  it  is  full  grown,  reduce  this  schedule 
by  one  quarter. 

Examples:     A  tree  20x30 6  ounces  for  purple. 

4.5  for  red,  yellow  and  black. 

30x40 12  ounces  for  purple. 

9.0  for  red,  yellow  and  black. 

SODIUM  CYANIDE. 

Mr.  Woglum  has  demonstrated  that  sodium  cyanide  is  equally  as 
satisfactory  as  the  potassium,  both  in  generating  properties  and  efficiency 
in  killing  the  scale;  and  since  it  will  be  apparently  cheaper  than  the 
potassium  it  seems  probable  that  it  may  sooner  or  later  come  into  very 
general  use.  Heretofore,  the  experience  with  sodium  cyanide  has  not 
been  satisfactory  for  the  reason,  chiefly,  that  the  product  was  not  pure 
enough.  "What  has  been  passing  for  98  to  100  per  cent  sodium  cyanide 
has  been  a  98  to  100  per  cent  purity  in  terms  of  potassium  cyanide, 
whereas,  if  we  accept  potassium  as  a  basis  of  purity,  the  sodium  cyanide 
should  be  126  to  133  per  cent  pure.  It  is  unfortunate  that  this  above-a- 
hundred  per  cent  purity  should  have  got  started,  but  since  we  are 
accustomed  to  potassium  as  a  standard  possibly  it  is  justifiable.  Any- 
way, all  we  need  to  know  is  that  a  pound  of  chemically  pure  sodium 
cyanide  contains  about  one  third  more  cyanide  or  cyanogen  than  the 
potassium,  and  will  thus  produce  more  gas. 

FORMULA  FOR  SODIUM  CYANIDE. 

Since  there  is  more  cyanide  or  cyanogen  in  a  pound  of  sodium  cyanide 
than  in  a  pound  of  potassium  cyanide,  it  will  require  a  proportionally 
greater  amount  of  acid.  One  of  the  uses  of  water  in  the  generation  of 
hydrocyanic  acid  gas  is  to  dissolve  the  residual  sulphate  and  thus  pre- 
vent it  from  coating  the  cyanide  not  yet  generated  or  reached  by  the 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  509 

acid.  In  the  case  of  sodium  cyanide  there  is  approximately  one  third 
less  of  the  sulphate  formed,  and  consequently  the  water  may  be  reduced 
about  one  third. 

Therefore,  the  proportions  of  cyanide  acid  and  water  will  differ  in  case 
sodium  cyanide  is  used,  and  the  formula  that  has  been  found  to  be 
satisfactory  is: 

Sodium  cyanide 1  part  by  weight. 

Acid 1$  parts  by  volume. 

Water    2  parts  by  volume. 

It  should  be  noted  that  in  case  sodium  cyanide  is  used  all  dosage  tables 
should  be  reduced  one  quarter. 

ADULTERANTS. 

The  commonest  adulterant  of  cyanides  is  sodium  chloride  or  common 
salt,  and  this  is  likely  to  get  into  sodium  cyanide,  particularly  in  large 
amounts.  The  presence  of  this  salt  produces  a  reaction  in  which  hydro- 
chloric acid  is  formed  and  this  acts  in  turn  directly  upon  the  hydrocyanic 
acid  gas,  thus  decomposing  it.  In  order  to  avoid  this  adulterant  a  high 
degree  of  purity  should  be  insisted  upon,  and  this,  stated  in  terms,  of  the 
potassium  salt  should  be  124  to  133  per  cent  pure. 

COMPARATIVE  COST  OF  SODIUM  AND  POTASSIUM  CYANIDE. 

A  good  sodium  cyanide  can  be  bought  for  27  or  28  cents  per  pound  as 
against  potassium  at  about  25  cents.  It  requires  a  little  more  acid  for 
the  sodium  so  that  the  acid  bill  is  higher  and  the  cost  per  pound  of 
cyanide  is  higher.  But  since  one  pound  of  the  sodium  will  generate  as 
much  as  one  and  a  quarter  pounds  of  the  potassium,  the  cost  is  really 
in  favor  of  the  sodium  cyanide,  and  this,  if  calculated  out,  will  be  found 
to  amount  to  from  1J  to  3^  cents  per  pound. 

FORMULA  FOR  POTASSIUM  CYANIDE. 

The  proportions  of  cyanide,  acid  and  water  that  have  been  found  to 
produce  the  greatest  amount  of  gas  are : 

Cyanide   1  oz.  avoirdupois. 

Acid    1  fluid  oz. 

Water 1 3  fluid  ozs. 

The  water  and  acid  are  first  placed  in  an  earthenware  vessel  and  the 
cyanide  added. 

EXPOSURE. 

The  usual  exposure  is  from  45  minutes  to  1  hour. 


510  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

SEASON  FOR  FUMIGATING. 

The  fumigating  season  extends  from  August  to  January.  The  fruit 
is  more  susceptible  to  injury  until  it  attains  about  the  size  of  a  walnut. 

Fumigation  during  extremes  of  temperature  (above  70°  and  below 
35°  F.)  may  injure  foliage  and  fruit,  or  during  a  high  wind. 

TENTING  MATERIAL. 

To  secure  the  tightest  possible  material  is  good  economy.  If  maxi- 
mum dosages  are  used  with  old  leaky  tents,  it  may  be  necessary  to  reduce 
the  dosage  with  the  tighter  material.  And  the  reduction  from  the  given 
schedules  should  not  be  made  the  same  for  all  sizes  of  trees,  because,  as 
the  tenting  material  becomes  tighter,  the  schedule  should  approach 
more  nearly  that  of  the  volume  basis. 

MEASUREMENT  OF  TENTS. 

The  distance  over  the  tented  tree  may  be  obtained  by  having  the  tents 
marked  according  to  the  Morrill  system,  or  any  other,  and  the  distance 
around  secured  by  a  tape  or  accurate  pacing. 

The  following  tables  are  based  upon  the  formula  given  above.  The 
schedule  for  the  purple  scale  corresponds  in  general  with  that  of  "Wog- 
lum's  schedule  No.  1,  and  those  for  the  red,  yellow  and  black  are  on  the 
basis  of  three  quarters  of  this  schedule : 

SCHEDULE  FOR  PURPLE  SCALE. 
Circumference  trees  16-56  feet. 
16    18    20   22    24    26    28    30    32    34    36    38    40     42     44     46     48     50     52     54     56 


10 

H 

14 

2 

2 

2 

24 

24 

3 

3 

(Distance  around.) 

3      3* 

12 

2 

2 

24 

3 

3 

3 

34 

34 

34    4"    4* 

14 

24 

3 

3 

34 

4 

4 

4 

4*    4*    5"     5* 

16- 

H 

4 

4 

44 

5 

5 

5|    6"    6       6j     7 

18  | 

4 

44 

4I 

5 

54 

6      6      6*     7       7       7* 

20  I 

5 

54 

6 

6 

6*    7      7|     8       8       8*     9 

22  g 

6 

64 

7 

7"  n  8"   8     84   9"   94  10 

- 

24| 

7 

71 
'2 

8      8|    9       94  10     10     10*,   11 
84    9      9*  10     IO4  11     11}  12 
9*    10  10*   H     llj  12     12"    13 

114 

26  5 

8 

12|  13 

28 

14     141  15 

30 

"  104  ll"   11*   12     13     13*  14 
12     12|  13     14     14j  15 

14*  15     154  16 

32 

15j  16     17     174 

SCHEDULE  FOR  PURPLE  SCALE. 
Circumference  trees  40-80  feet. 
40    42    44   46    48    50    52    54    56    58    60    62    64     66     68     70     72     74     76     78     80 


154  16*  17    17*  184  19    20 

"  184  19"  20    204  21|  22 


(Distance  around.) 


20    204  21*  22    23    24     25 

20*  21*  22"  23    24    244  25*  26 

2l|  22*  23*  24    25    26     26*  27*  284 

23    23*  24*  25*  26    27     28"   28j  29£  30* 

46  1  24*  25*  26*  27*  28*  294   30     31     32  33     34 

48  1  "  25*  26*  27 J  28*  29*  304  314  32*  334  344  35 

50  8  28    29"  30"  31"  32     33     34  35     36     37     38 

52  "  30    31    32     33     34     35  36     37     38     394  4<>4 

54  32    33     344  35*  36*  37*  38J  39J  40     41      42 

56  34*  354   36|  38|  39"   40     41     42*,   434    444 


i  7 


Bulletin  214]  CITRUS  FRUIT  INSECTS.  511 

SCHEDULE   FOR  RED,    YELLOW,   AND   BLACK   SCALES. 
Circumference  trees   16-56  feet. 
16    18    20    22    24    26    28    30    32    34    36    38    40     42     44     46     48     50     52     54     56 

(Distance  around. ) 

io    i    i    i    i    i    14  n  2    2    2    24 

12  1      1      1£    2      2      2      2i    2*  24  3  3 

14  14    2     '2      2|    3      3      3"  3"  3  34  4 

16-  d    2|    3      3      3      3HM  4  4|4i  54 

18  «  3      3      3      3|    4"  4  4  4j  5  5  54 

20  °  34    4      4"    4  44  5  54  6  6  6* 

22  §  4      4i    5  5"  54  6"  6  64  64 

24  I  5"    54  6  6  64  64  7  7"     74     8       84 

26  3  6  6  64  64  7"  74  8       8}     9       9       94 

28  64  64  74  8  84  9       9"     94   10     10|   11 

30  7|  8  84  9"  94  10     104  104  11     114  12 

32  9  9  94  104   10 1    11"   114   12     12|  13 

SCHEDULE   FOR  RED,    YELLOW,   AND   BLACK   SCALES. 
Circumference  trees  40-80  feet. 
40    42    44   46    48    50    52    54    56    58    60    62    64     66     68     70     72     74     76     78     80 

(Distance  around.) 

34  10  10  104  11  114  12  124  13  134  14  15 

36  11  111  12  124  13  134  14  15  15  16  16 

38  12"  13  13"  14  15"  15  16  16  17  18  18i 

40-:  13  14  15  15  16  16  17  18  18  19  19 

42  I  15  154  16  164  17  18  184  19  194  204  21 

44  %  16"  17  17  18  19  19"  20  21  21  22  224 

46  S  18  19  194  204  21  22  22  23  24  244  244 

48  1  19  194  20j  21  22  224  234  24  25"  254  26 

50  g  21"  21"  22  23  24  244  254  26  27"  274  28J 

52  224  23  24  244  254  26"  27  274  284  294  30 

54  "  24  244  254  264  274  28  284  294  30"  304  314 

56  254  264  27  284  29  30"  304  31  32"  33„ 


INSPECTION  AND  QUARANTINE. 

In  most  of  the  counties  of  the  citrus  belt  there  are  special  ordinances 
pertaining  to  the  quarantine  of  certain  citrus  fruit  pests.  The  grower 
or  nurseryman  should  consult  his  county  horticultural  commissioner 
regarding  these  before  making  any  interchange  of  nursery  or  other 
stock.  The  section  of  the  state  law  relating  to  the  duties  of  county 
boards  of  horticulture,  approved  March  6,  1909,  is  given  below : 

Section  2322a.  It  shall  be  the  duty  of  the  county  horticultural  commissioner  in 
each  county,  whenever  he  shall  deem  it  necessary,  to  cause  an  inspection  to  be  made 
of  any  premises,  orchards  or  nursery  or  trees,  plants,  vegetables,  vines,  or  fruits,  or 
any  fruit-packing  house,  storeroom,  salesroom,  or  any  other  place  or  article  in  his 
jurisdiction,  and  if  found  infected  with  infectious  diseases,  scale  insects,  or  codling 
moth,  or  other  pests  injurious  to  fruit,  plants,  vegetables,  trees,  or  vines,  or  with  their 
eggs  or  larva?,  or  if  there  is  found  growing  thereon  the  Russian  thistle  or  saltwort, 
Johnson  grass  or  other  noxious  weeds,  he  shall  in  writing  notify  the  owner  or  owners, 
or  person  or  persons  in  charge,  or  in  possession  of  the  said  places,  or  orchards  or 
nurseries,  or  trees,  or  plants,  vegetables,  vines,  or  fruits  or  article  as  aforesaid,  that 
the  same  are  infected  with  said  diseases,  insects  or  other  pests,  or  any  of  them,  or 
their  eggs  or  larvae,  or  that  the  Russian  thistle  or  saltwort,  Johnson  grass  or  other 
noxious  weeds  is  growing  thereon,  and  require  such  person  or  persons,  to  eradicate 
or  destroy  the  said  insects,  or  other  pests,  or  their  eggs  or  larvae,  or  Russian  thistle 
or  saltwort,  Johnson  grass,  or  other  noxious  weeds  within  a  certain  time  to  be  therein 
specified.  Said  notices  may  be  served  upon  the  person  or  persons,  or  either  of  them, 
owning  or  having  charge,  or  having  possession  of  such  infested  place  or  orchard,  or 
nursery,  or  trees,  plants,  vegetables,  vines,  or  fruit,  or  articles,  as  aforesaid,  or 
premises  where  the  Russian  thistle  or  saltwort,  or  Johnson  grass,  or  other  noxious 

6— b214 


512  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

weeds  shall  be  growing,  or  upon  the  agents  of  either,  by  any  commissioner,  or  by  any 
person  deputed  by  the  said  commissioner  for  that  purpose  in  the  same  manner  as  a 
summons  in  a  civil  action  ;  provided,  however,  that  if  any  such  infected  or  infested 
articles,  property  or  premises  as  hereinabove  specified  belong  to  any  non-resident 
person  and  there  is  no  person  in  control  or  possession  thereof  and  such  non-resident 
person  has  no  tenant,  bailee,  depositary  or  agent  upon  whom  service  can  be  had ;  or, 
if  the  owner  or  owners  of  any  such  articles,  property  or  premises  can  not  after  due 
diligence  be  found,  then  such  notice  may  be  served  by  posting  the  same  in  some 
conspicuous  place  upon  such  articles,  property  or  premises,  and  by  mailing  a  copy 
thereof  to  the  owner  thereof  at  his  last  known  residence,  if  the  same  is  known  or  can 
be  ascertained.  Any  and  all  such  places,  or  orchards,  or  nurseries,  or  trees,  plants, 
shrubs,  vegetables,  vines,  fruit,  or  articles  thus  infested,  or  premises  where  the 
Russian  thistle,  or  saltwort,  or  Johnson  grass,  or  other  noxious  weeds  shall  be  grow- 
ing, are  hereby  adjudged  and  declared  to  be  a  public  nuisance ;  and  whenever  any 
such  nuisance  shall  exist  at  any  place  within  his  county,  and  the  proper  notice 
thereof  shall  have  been  served,  as  herein  provided,  and  such  nuisance  shall  not  have 
been  abated  within  the  time  specified  in  such  notice,  it  shall  be  the  duty  of  the  county 
horticultural  commissioner  to  cause  said  nuisance  to  be  at  once  abated,  by  eradicating 
or  destroying  said  diseases,  insects,  or  other  pests,  or  their  eggs,  or  larvae,  or  Russian 
thistle  or  saltwort,  or  Johnson  grass  or  other  noxious  weeds.  The  expense  thereof 
shall  be  a  county  charge,  and  the  board  of  supervisors  shall  allow  and  pay  the  same 
out  of  the  general  fund  of  the  county.  Any  and  all  sum  or  sums  so  paid  shall  be  and 
become  a  lien  on  the  property  and  premises  from  which  said  nuisance  has  been 
removed  or  abated  in  pursuance  of  this  chapter.  A  notice  of  such  lien  shall  be  filed 
and  recorded  in  the  office  of  the  county  recorder  of  the  county  in  which  the  said  prop- 
erty and  premises  are  situated,  within  thirty  days  after  the  right  to  the  said  lien  has 
accrued.  An  action  to  foreclose  such  lien  shall  be  commenced  within  ninety  days 
after  the  filing  and  recording  of  said  notice  of  lien,  which  action  shall  be  brought  in 
the  proper  court  by  the  district  attorney  of  the  county  in  the  name  and  for  the  benefit 
of  the  county  making  such  payment  or  payments,  and  when  the  property  is  sold, 
enough  of  the  proceeds  shall  be  paid  into  the  county  treasury  of  such  county  to 
satisfy  the  lien  and  costs ;  and  the  overplus,  if  any  there  be,  shall  be  paid  to  the 
owner  of  the  property,  if  he  be  known,  and  if  not,  into  the  court  for  his  use  when 
ascertained.  The  county  horticultural  commissioner  is  hereby  vested  with  the  power 
to  cause  any  and  all  such  nn Usances  to  be  at  once  abated  in  a  summary  manner. 


STATION    PUBLICATIONS    AVAILABLE    FOR    DISTRIBUTION, 


REPORTS. 


1896.  Report  of  the  Viticultural  Work  during  the  seasons  1887-93,  with  data  regard- 

ing the  Vintages  of  1894-95. 

1897.  Resistant  Vines,  their  Selection,  Adaptation,  and  Grafting.     Appendix  to  Viti- 

cultural Report  for  1896. 

1902.  Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

1903.  Report  of  the  Agricultural  Experiment  Station  for  1901-03. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station  for  1903-04. 


BULLETINS. 


Reprint.     Endurance  of  Drought  in  Soils  ofj  No.   186. 
the  Arid  Region.  187 

No.   128.  Nature,  Value,  and  Utilization  ofj 

Alkali  Lands,  and  Tolerance  ofj  188. 

Alkali.      (Revised  and  Reprint,] 
1905.)  •]  189. 

133.  Tolerance    of   Alkali   by  Various 

Cultures.  j  190. 

147.   Culture  Work  of  the  Sub-stations.  191. 

149.   California  Sugar  Industry.  192. 

151.  Arsenical  Insecticides. 

153.   Spraying  with  Distillates.  193. 

159.  Contribution  to  the  Study  of  Fer- 
mentation. 

161.  Tuberculosis  in  Fowls.  (Reprint.)  194. 

162.  Commercial  Fertilizers.     (Dec.  1, 

1904.)  195. 

165.  Asparagus    and   Asparagus    Rust 

in  California.  197. 

167.  Manufacture    of    Dry    Wines    in 

Hot  Countries. 

168.  Observations  on  Some  Vine  Dis- 

eases in  Sonoma  County.  198. 

169.  Tolerance  of  the  Sugar  Beet  for  199. 

Alkali.  200. 

170.  Studies  in  Grasshopper  Control. 

171.  Commercial     Fertilizers.       (June  201. 

30,  1905.) 

172.  Further  Experience  in  Asparagus  202. 

Rust  Control. 
174.  A  New  Wine-cooling  Machine.  203. 

176.  Sugar  Beets  in  the  San  Joaquin 

Valley.  204. 

177.  A   New  Method   of  Making  Dry 

Red  Wine.  205. 

178.  Mosquito  Control. 

179.  Commercial    Fertilizers.       (June,  206. 

1906.) 

180.  Resistant  Vineyards.  207. 

181.  The  Selection  of  Seed- Wheat.  208. 

182.  Analysis     of     Paris     Green     and  209. 

Lead    Arsenic.       Proposed    In-  210. 

secticide  Law. 

183.  The  California  Tussock-Moth.  211. 

184.  Report   of  the   Plant   Pathologist 

to  July  1,  1906.  212. 

185.  Report     of     Progress     in     Cereal  213. 

Investigations. 


The   Oidium  of  the  Vine. 

Commercial  Fertilizers.  (Janu- 
ary   1907.) 

Lining  of  Ditches  and  Reservoirs 
to  Prevent  Seepage  and  Losses. 

Commercial  Fertilizers.  (June, 
1907.) 

The  Brown  Rot  of  the  Lemon. 

California  Peach  Blight. 

Insects  Injurious  to  the  Vine  in 
California. 

The  Best  Wine  Grapes  for  Cali- 
fornia ;  Pruning  Young  Vines  ; 
Pruning  the  Sultanina. 

Commercial  Fertilizers.  (Dec, 
1907.) 

The  California  Grape  Root- 
Worm. 

Grape  Culture  in  California ; 
Improved  Methods  of  Wine- 
making  ;  Yeast  from  California 
Grapes. 

The  Grape  Leaf-Hopper. 

Bovine  Tuberculosis. 

Gum  Diseases  of  Citrus' Trees  in 
California. 

Commercial  Fertilizers.  (June, 
1908.) 

Commercial  Fertilizers.  (Decem- 
ber, 1908.) 

Report  of  the  Plant  Pathologist 
to  July  1,  1909. 

The  Dairy  Cow's  Record  and  the 
Stable. 

Commercial  Fertilizers.  (Decem- 
ber,   1909.) 

Commercial  Fertilizers.  (June, 
1910.) 

The  Control  of  the  Argentine  Ant. 

The  Late  Blight  of  Celery. 

The  Cream  Supply. 

Imperial  Valley  Settlers'  Crop 
Manual. 

How  to  Increase  the  Yield  of 
Wheat  in  California. 

California  White  Wheats. 

The    Principles    of    Wine-making. 


CIRCULARS. 


No.      1.  Texas  Fever. 

5.  Contagious  Abortion  in  Cows. 
7.  Remedies  for  Insects. 
9.  Asparagus  Rust. 

11.  Fumigation  Practice. 

12.  Silk  Culture. 

15.  Recent    Problems    in    Agriculture. 

What  a  University  Farm  is  For. 

17.  Why  Agriculture  Should  be  Taught 

in  the  Public  Schools. 
19.  Disinfection  of  Stables. 

29.  Preliminary    Announcement    Con- 

cerning Instruction  in  Practical 
Agriculture  upon  the  University 
Farm,  Davis,  Cal. 

30.  White  Fly  in  California. 

32.  White   Fly  Eradication. 

33.  Packing    Prunes    in    Cans.      Cane 

Sugar  vs.  Beet  Sugar. 

36.  Analyses  of  Fertilizers  for  Con- 
sumers. 

39.  Instruction  in  Practical  Agricul- 
ture at  the  University  Farm. 


No.   46.   Suggestions   for    Garden   Work   in 
California  Schools. 

47.  Agriculture  in  the  High  Schools. 

48.  Butter  Scoring  Contest,   1909. 

50.  Fumigation    Scheduling. 

51.  University  Farm  School. 

52.  Information  for  Students  concern- 

ing the   College   of  Agriculture. 

53.  Announcement  of   Farmers'    Short 

Courses  for   1910. 

54.  Some     Creamery     Problems     and 

Tests. 

55.  Farmers'  Institutes  and  University 

Extension  in  Agriculture. 

58.  Experiments  with  Plants  and  Soils 

in     Laboratory,     Garden,     and 
Field. 

59.  Tree      Growing      in      the      Public 

Schools. 

60.  Butter  Scoring  Contest,   1910. 

61.  University  Farm  School. 

62.  The  School  Garden  in  the  Course 

of  Study. 


